Netflix!
I also make good use of the Craigslist app (called Craigsphone), ebay, Real Solitaire, Chess, SpeedtestX HD, Dictionary.com app, Virtuoso Piano app, Pac-Sam (game), Touch Hockey (air hockey game), Blue Block (puzzle game).
I'm a reader, but I really can't swing reading on an electronic device. It simply doesn't mimic the reading experience. I suppose I'm a bit of a snobbish bibliophile, but it just seems odd to read a classic on an iPad, or even on a computer. That said, I do have the Kindle app and a few free book downloads I found on Amazon, and I think it would do in a pinch if I simply had no room for reading material in my bag. I'd never pay for an eBook.
If you like Edgar Allan Poe, there's a free app that has all of his works, both prose and poetry, for those times that you just really need to hear the BELLS, BELLS, BELLS.
The Pages app is also decent, though it could stand to be a bit more capable as a word processor than it is.