
I've got the Sky+ and SkyGo apps, one allows me to watch stuff (handy for catching up with the news on my daily commute), and the other lets me remote record things if I've forgotten to set them up.
The Argos one is handy, depending on how much/often you shop there, it allows you to register your local/favourite store and automatically advises stock levels for whatever it is you're looking at.
Other than those, (and a couple of sports ones), most of mine aren't used.
Oh I do also have a Kindle app, but as I now also have a kindle I don't tend to use it.
(I downloaded the Battersea Cats and Dogs home app, when a friends best friend went to the bridge - but get depressed when I look at it, so don't tend to use that one much either).
T