After doing lots of research I’ve spent time to get my top 50 applications for an iDevice so lets get started.

Google+ (Free)

Real-life sharing rethought for the web, wherever you are. Google+ for mobile makes sharing the right things with the right people a lot simpler.

LinkedIn (Free)

Get on-the-go access to your professional network with LinkedIn for iPhone. Find and connect with more than 135M members worldwide, read the latest industry news, keep up-to-date with your groups, and share content with your network from anywhere.

Foursquare (Free)

foursquare helps you explore the world around you. Keep up with friends, get insider tips, and unlock discounts and rewards. While on the go, you can easily tell friends where you are, share pictures, get their comments (“I’m right around the corner, I’ll stop by to say hello”), and get insider tips (“order the Lobster Ravioli; it’s the best dish by far.”). Tons of places offer discounts and freebies to foursquare users, and you earn points and badges for doing the things you love.

Other noteworthy social networking app: Path (Free)

WhatsApp (Free)

WhatsApp Messenger is a cross-platform smartphone messenger currently available for iPhone, Android, BlackBerry and Nokia phones. The application utilizes push notifications to instantly get messages from friends, colleagues and family. Switch from SMS to exchange messages, pictures, audio notes and video messages with WhatsApp users at no cost.

Skype (Free)

Call, video call and instant message anyone else on Skype for free with Skype for your iPhone or iPod touch. Plus call and text your Contacts (or any other number) at Skype’s low rates. It’s great value with Skype Credit.

BeeJiveIM With Push ($4.99)

Stay connected to all your instant messaging buddies anywhere you go! BeejiveIM (pronounced \bē-hīv\ IM) keeps you in touch with your friends on AIM®/MobileMe®, MSN®/Windows Live®, Yahoo!®, GoogleTalk®, Facebook, MySpace and Jabber… all at the same time, all on your iPhone or iPod Touch.

Free Alternative: IM+

Reading:

Kindle (Free)

The Kindle app is optimized for the iPad, iPhone, and iPod touch, giving users the ability to read Kindle books, newspapers, magazines, textbooks and PDFs on a beautiful, easy-to-use interface.

iBooks (Free)

iBooks is an amazing way to download and read books. iBooks includes the iBookstore, where you can download the latest best-selling books or your favorite classics – day or night. Browse your library on a beautiful bookshelf, tap a book to open it, flip through pages with a swipe or a tap, and bookmark or add notes to your favorite passages.

Reeder ($2.99)

Google Reader Client.

Free Alternative: Google Reader web app (Free)

Zinio (Free)

Introducing Zinio, a better way than ever to explore, read and shop for the world’s best magazines on your iPad. Zinio now has more magazines than ever, and a new app built to make it easier to read your favorites anytime and anywhere. Zinio is the ultimate app for people who love magazines. Access thousands of titles, tens of thousands of issues, and millions of pages of the world’s best digital content. Read what you like!

PressReader (Free)

Over 2,000 full-content newspapers from 95 countries in 51 languages in just one app!

Flipboard (Free)

Named Apple’s iPad App of the year and one of TIME’s Top 50 Innovations, Flipboard creates a personalized magazine out of everything being shared with you, from Instagram photos and Facebook updates to Tumblr posts and articles from your favorite publications.

Zite (Free)

Zite is a free personalized magazine for your iPad that automatically learns what you like and gets smarter every time you use it. Zite delivers all the great news, articles, blogs, and videos you want – and helps you discover new stuff that you’ll love.

Instapaper ($4.99)

Save web pages for later offline reading, optimized for readability on your iPhone or iPod touch’s screen. Featured by Apple and critically acclaimed by top blogs, newspapers, and magazines!

Photo & Video:

Camera+ ($0.99)

Whether you’re a seasoned photographer or someone who’s barely touched a camera, Camera+ will make you love taking photos.

iMovie ($4.99)

Make beautiful HD movies anywhere with iMovie, the fast and fun moviemaking app for iPhone, iPod touch, and iPad. Designed for the Multi-Touch screen, iMovie puts everything you need to tell your story at your fingertips. Browse and play projects in the Marquee view. Make a movie in minutes by adding video, photos, music and sound effects. Then give it the Hollywood treatment by adding a theme, titles and transitions. And you can share share your movie with the world – right from iMovie.

Instagram (Free)

It’s a free, fun, and simple way to make and share gorgeous photos on your iPhone. Pick from one of several gorgeous filtered effects or tilt-shift blur to breathe a new life into your mobile photos. Transform everyday moments into works of art you’ll want to share with friends and family.

Alternative: Hipstamatic ($1.99), Snapseed ($4.99)

Music:

Shazam (Free)

Hear a song you don’t know? Shazam identifies it instantly.

Free Alternative: SoundHound (Ad Supported)

Pandora Radio (Free)

Pandora Radio is free personalized radio that only plays music you’ll love. Just start with the name of one of your favorite artists, songs or classical composers and Pandora will create a custom “station” that plays similar music.

TuneIn Radio Pro ($0.99)

TuneIn is a new way to listen to the world through live local and global radio from wherever you are. Whether you want music, sports, news or current events, TuneIn offers over 50,000 stations and 120,000 shows for you to choose from. The TuneIn Radio Pro app for iPhone, iPad and iPod touch puts this entire experience in the palm of your hand with the added benefit of recording what you’re listening to.

Free Alternative: TuneIn Radio

Spotify (Free)

Get free access to Spotify Premium now! With Premium you’ll get access to 15 million tracks from thousands of albums and artists on your iPhone, iPod Touch & iPad. If you haven’t tried Premium before, you can try it on your mobile for 48-hours, completely free. You don’t even have to enter credit card details. Simply download this app and log in.

djay for iPhone & iPod touch ($0.99)

Ready to rock your next party? The premier DJ app and winner of the 2011 Apple Design Award for iPad now fits in your pocket: introducing djay for iPhone & iPod touch!

GarageBand ($4.99)

GarageBand turns your iPad, iPhone and iPod touch into a collection of Touch Instruments and a full-featured recording studio — so you can make music anywhere you go. Use Multi-Touch gestures to play pianos, organs, guitars, drums, and basses. They sound and play like their counterparts, but let you do things you could never do on a real instrument. Enjoy a full range of Smart Instruments that make you sound like a pro — even if you’ve never played a note before. Plug an electric guitar into your iPad, iPhone or iPod touch and play through classic amps and stompbox effects. Use the built-in microphone or a guitar to record, or capture any performance. Then mix up to eight tracks to create a song you can share.

Finance:

iXpenseIt ($1.99)

iXpenseIt simplifies daily expense tracking and monthly budgeting. With iXpenseIt, it’s never been easier to stay current on your personal budget or for business users, to get faster reimbursements. Store photo receipts is a snap. Enter expense data anywhere, anytime within seconds. Powerful reporting provides insight to where your money went and find new ways to save.

Lemon – Receipts Refreshed (Free)

Lemon.com is the best way to organize all your purchases into one simple place. Easily scan your paper receipts and we’ll turn the images into useful information that’s taggable and searchable so you can get organized and know where you’re spending your money.

Productivity:

Numbers ($9.99)

Numbers is the most innovative spreadsheet app ever designed for a mobile device. Built from the ground up for iPad, iPhone, and iPod touch, it lets you make compelling spreadsheets in minutes — with tables, charts, photos, and graphics — using just your fingers. Choose from over 250 easy-to-use functions. Enter data and explore results with sliders, steppers, pop-ups, and intelligent keyboards.

Pages ($9.99)

Pages is the most beautiful word processor you’ve ever seen on a mobile device. This powerful app has been exclusively designed for the iPad, iPhone and iPod touch. Create, edit, and view documents wherever you are. Use dictation in iOS 5 on your iPhone 4S to easily create and edit documents.

Keynote ($9.99)

Keynote is the most powerful presentation app ever designed for a mobile device. Built from the ground up for iPad, iPhone, and iPod touch, it makes creating a world-class presentation — complete with animated charts and transitions — as simple as touching and tapping. Use full-screen view to present right on your iPad, iPhone, or iPod touch. Or use video mirroring to present it on an HDTV, and preview your slides and notes on your device using the presenter display.

Wunderlist (Free)

The Wunderlist mobile app for iPhone and iPod Touch will boost your productivity. Organize your to-do lists on the go and synchronize them with your free Wunderlist account. View and modify your tasks on Windows, Mac, Linux,iPad, Android and the Web.

TeamViewer (Free) TeamViewer provides easy, fast and secure remote access to Windows, Mac and Linux systems. Alternative: LogMeIn (Free)
Evernote (Free)

Evernote turns the iPhone, iPod Touch and iPad into an extension of your brain, helping you remember anything and everything that happens in your life. From notes to ideas to snapshots to recordings, put it all into Evernote and watch as it instantly synchronizes from your iPhone to your Mac or Windows desktop.

Health & Fitness:

Sleep Cycle Alarm Clock ($0.99)

An alarm clock that analyzes your sleep patterns and wakes you in the lightest sleep phase – a natural way to wake up where you feel rested and relaxed.

Runkeeper (Free)

RunKeeper uses the GPS technology found in the iPhone to track your fitness activity, giving you comparable results to an expensive GPS watch. Now, you can also enter your activities manually, including your treadmill runs too!

Travel:

Google Translate (Free)

Translate words and phrases between more than 60 languages using Google Translate for iOS. For most languages, you can speak your phrases and hear the corresponding translations.

FlightTrack Pro ($9.99)

Import flight data automatically from any airline confirmation email and get push alerts with real-time changes to your flight. Get real-time flight itinerary updates, and beautiful, zoomable maps that even work offline. FlightTrack Pro has everything you need to stay on top of your trip.

Alternative: FlightTrack ($4.99)

Yelp (Free)

Looking for a burrito joint open now? An Irish pub nearby? A gas station you can drive to before your tank hits empty? Yelp for your iPhone is here to help. Use us to search for places to eat, shop, drink, relax and play then read reviews from an active community of locals in the know.

Urbanspoon (Free)

Can’t decide where to eat? Urbanspoon can help. SHAKE your iPhone and the Urbanspoon slot machine will suggest a restaurant. See what’s NEARBY in your ‘hood, or BROWSE a comprehensive list of restaurants. Make a RESERVATION, and expand your DINELINE by checking in. See what your FRIENDS like.

XE Currency (Free)

Convert every world currency on-the-go with the universally optimized XE Currency App for iPhone and iPad. It features live currency rates, charts, and even stores the last updated rates, so it works when the Internet doesn’t.

Entertainment:

Neflix (Free)

Just download this free app and you can instantly watch TV shows & movies streaming from Netflix.

Flixster (Free)

Movies by Flixster is the #1 movie app to watch movie trailers, find showtimes, get critics reviews from Rotten Tomatoes, and share your movie ratings with your friends.

Alternative: IMDB (Free)

Brushes ($4.99) Brushes is a painting application designed from scratch for the iPhone and iPod touch. Featuring an advanced color picker, several realistic brushes, layers, extreme zooming, and a simple yet deep interface, it is a powerful tool for creating original artwork on your mobile device.
Utilities:

Find My iPhone (Free)

If you misplace your iPhone, iPad, iPod touch, or Mac, the Find My iPhone app will let you use another iOS device to find it and protect your data. Simply install this free app on another iOS device, open it, and sign in with your Apple ID. Find My iPhone will help you locate your missing device on a map.You can then choose to display a message or play a sound, remotely lock your device, or erase your data on it.

1Password for iPhone ($5.99)

1Password will securely store your important information and can automatically log you into websites with a single tap. There’s no need to remember the username, password, or even the website address.

RedLaser Barcode Scanner and QR Code Reader (Free)

RedLaser – Impossibly accurate barcode scanning.

Alternative: Barcode Scanner For Shopping ($0.99)

Onavo (Free)

Onavo’s app connects your iPhone to our cloud-based technology, dubbed the “magical shrinking machine”. It’s totally seamless – once you install it you can go back to using your phone as before. In the background, your data usage from all apps is compressed so that you get more bang for your buck, doubling and even tripling your data plan.

CamCard ($6.99)

CamCard is a fantastic business card reader with high recognition accuracy. Simply take a picture of a business card, CamCard recognizes the contact information and saves it Card Holder or iPhone Addressbook. Then feel at ease to manage and make correspondence to all the contacts.

You can check out the CamCard Lite version before buying the full version.

CamScanner+ ($4.99)

With CamScanner, your iPhone is actually a portable scanner, with which all your paper documents, receipts, notes, whiteboard discussions can be archived anywhere at anytime. Our Smart Image cropping and Image enhancement algorithm ensures the scanned images perfectly clear and recognizable. With OCR technology, text within PDF files will be searchable.

You can check out CamScanner Free before buying the full version.

Convertbot ($1.99)

Convertbot is a unit conversion robot. Convert currency, length, mass, time and much more in an exciting new way! Converting numbers will never again be a mundane task. In addition to its innovative interface, our robot is smart enough to convert to and from mixed units. Are you 5 foot 9 inches tall? Other converters require you to convert that to 5.75 ft in your head before being able to enter it. Convertbot allows mixed units like Foot + Inches, Pounds + Ounces, and more!

Speedtest.net Mobile Speed Test (Free)

Use Speedtest.net for easy, one-tap connection testing in under 30 seconds—accurate anywhere thanks to our global network.

That’s it for now. We’ll continue to update this post as and when we find new must-have apps. We’ve also not included apps in categories such as Lifestyle, Education etc. We hope to update this list with apps in those categories shortly. We’ll post an article on our top games for iPhone and publish a similar list for the iPad.