I am not, as you may know, an Apple person BUT, these are great. Don't know if all of them are available for an Apple device or what they would cost. I know a good few of them are available for IPhone as well though.
Viber - for free calls to everyone else in your phonebook who has it. Don't know the trend in the UK, but in Sweden loads of peeps have it.
Whatsapp messenger - free text messages, MMS or audio files. Same as with Viber. Don't know the UK situation obviously.
Waze - great interactive navigation app. Much better than anything Apple has to offer...
Cerberus - to locate a missing/stolen device. I know Apple has a feature like this, but I'd bet my left arm this one is head and shoulders above.
Lookout - for safe browsing. Would strongly recommend ESPECIALLY for IPhone users since Safari has had a quite a lot of problems here.
Juicedefender - very easy to use and it helps you save your batterylife quite a lot with no real effort.
Evernote - everything you can possibly ask for, and more, when it comes to organization.
Dropbox - excellent for storing and sharing pics and vids.
Tasker - best app ever. You need to a bit of a cellphone nerd for it though. Makes your smartphone REALLY smart if you get the basic features of the app even.