The following list showcases our pick of the 40 best free iPhone apps, and includes iPhone applications for social networking, travel, news, photography, productivity and more.
If your favourites aren't covered, tell us all about them in the comments.

1. Facebook
Once an ugly duckling, but now - as of version 3 - a social-network-aware swan, Facebook is a triumph. The revised grid-based 'home screens' provide speedy access to regularly visited sections (news feed, notifications, and so on) and pages, and the experience is such that it in many ways beats the browser version.
Facebook

2. Gorillacam
Pretty much from nowhere, Gorillacam arrived in December 2009 from the creators of the Gorillapod tripods. It mashes together a slew of features to hugely improve an iPhone's camera (timer, multi-shot, spirit-level, on-screen grid, 'press anywhere' capture), meaning you can bin a half-dozen standalone apps that offer similar things.
Gorillacam

3. RunKeeper Free
The prospect of Nike+ but better and for free might sound unlikely, but that's what RunKeeper Free provides. The app uses an iPhone's GPS capabilities to track your jogging route, and provides mapping and details of pace and calories burned. Activities can be shared online, and treadmill runs can be entered manually.
Runkeeper

4. Stanza
Kindle's grabbed many 'electronic book' headlines, but an iPhone or iPod touch is a perfectly competent alternative - at least if you have the right app to hand. Stanza enables you to download books from various sources (many of which offer free titles), and you can transfer your own ePub, PDF or eReader titles from the free Stanza Desktop.
Stanza

5. Dropbox
Plenty of apps exist for transferring content between your computer and your device, but Dropbox is free and easier to use than most of its contemporaries. Dump files you want to sync in a folder on your computer and Dropbox for your device will enable you to access them, download them for offline viewing, and, in many cases, view them.
Dropbox

6. thetrainline
For anyone commuting by train, thetrainline is the free app to beat all others. Journey planning, offline results, timetables and a location-aware 'next train home' option are available via a clean, streamlined interface. The app's not quite as good as National Rail Enquiries, but it is very similar - and five quid cheaper.
thetrainline

7. Skype
It's imperfect and annoyingly lacks push notifications, but Skype is still an essential download. The interface is pleasingly simple and usable, enabling anyone with a Skype account to make free calls to other Skype users and cheap calls to anywhere in the world. If you're on Pay and Go, this is particularly handy, but the app also enables iPod touch users to utilise their devices for calls.
Skype

8. Movies
Although some aspects of cinema listings app Movies are  US-centric (notably regarding details on upcoming movies and DVDs), it succeeds where it matters. Select a film and the app figures out where you're located, lists nearby cinemas, and displays times your chosen film is showing. Efficiency can be further increased by pinning favourite cinemas to the top of the list.
Movies

9. TonePad
Virtual pianos and guitars are all very well, but purely digital musical toys are more suited to Apple handhelds. TonePad is the best of them, using a grid-based interface that enables you to turn notes on and off and compose pleasing and harmonious loops; your creations can be edited, saved and uploaded to share with other users.
Tonepad

10. Thomson Reuters News Pro
There are many free news apps, but Reuters News Pro offers a breadth of coverage that makes it a winner. Preferences enable you to tailor the app's output to the US, and the toolbar provides swift access to news, pictures, videos and stock markets coverage.
Reuters

11. Twitter (formerly Tweetie)
Tweetie was the iPhone Twitter client that other iPhone Twitter clients wanted to be. Its combination of polished interface, plentiful options and multi-account support meant everyone loved it - apart from cheapskates, because Tweetie wasn't free. Now, however, it is, because Twitter bought it, rebranded it as Twitter, and set fire to the price tag.
Twitter for iphone