TV catchup is well worth it
Thats shite now to be honest, was once good but hardly got any channels since it lost the court case.
If you have Sky then Sky Go and the Sky Remote app are great. Zeebox is a good TV Guide.
If you read a lot of blogs then Feedly is a great reader.
If you aren't a fan of the offy Twitter app (I'm not) then Hootsuite is a good alternative.
Whatapp is a good alternative to iMessage as lets you send texts/photos/vids free to each other and others using the app.
Shazam is great for identifying a clip of music.
BBC Weather app is better than the normal iPhone one I find.