Depends what you want to do.

The TomTom apps, although expensive, are as good as a proper TomTom in my opinion.
Cyclemeter is great for cycling (duh).
Accessing cloud storage is easy with things like Box and Dropbox. To Do lists have thousands of apps, I like Things. And it has a (Mac only) desktop version to link it up to as well.
Eurosport is good, as is the iPlayer, 4oD and Sky Go things for TV, provided you have wifi as they eat up data and battery over 3G.
Photography apps like Camera Bag, PhotoShop Express, PerfectlyClr and Slow Shutter are all cheap and good. Flickr is also surprisingly good, in my opinion.
If you go skiing or snowboarding there are loads of apps for that - I use Ski Tracks which tracks you, and doesn't use as much battery as most.
QuickOffice is good, but Pages is better for making word docs if you need to.

Posted By: APB, Jun 11, 10:23:43