Aldiko : IMO easily the best e-reader out there. Has a big library of both free and paid books.
Break the Bricks : one of those old arcade games, but in a modernized version
Drag Racing : Good game if you're a bit of a car nut. Lots of cars, lots of tuning options.
Dropbox : Very handy if you have dropbox on your PC as well.
Google Earth : This one doesn't need an explanation.
Note everything : Makes text notes, audio notes, video notes. Unfortunately it doesn't transfer them to the PC, so you might want to look into Evernote if you want to have the same notes cross-platform.
QR barcode scanner (by Warriors)
Rockplayer Lite : IMO one of the best video players. Plays just about every major movie format.
Solitaire (by Ken Magic) : I'm addicted to this one.
Wifi analyzer (by Farproc) : perfect tool for figuring out if someone else is on the same frequency, or for finding one that's still free. I used this app set my home Wifi to a channel that wasn't used in my immediate area, and it dramatically improved Wifi performance.