VLC is good but it may not be there for long. Angry Birds, Bento, Numbers, Cut the Rope HD, Geared, NASA app, Things (I use it on the Mac and it syncs which is useful), Google Earth is amazing with touch, Dropbox, Kindle, Epicurious (when you are thinking about what to make for tea), Pinball HD, Osmos, Sketchbook pro.
For a start.
I don’t store much music on my iPad as it is generally in the house. I do keep my copy of ‘Seasons’ film on it though when I want to pretend to be good at biking!