Favorite free iPad apps?

[mawhite63]

My husband got an iPad 2 for work and I've been teaching myself how to use it so I can show him LOL! I've been having a lot of fun with it. I've installed the productivity apps that he'll need like Dropbox, etc. There are so many apps out there it's a bit overwhelming. I don't want to muck up his icons with things he doesn't need, but I know there are probably some really useful ones I'm missing. What are some good free or really really cheap apps? He is allowed to use it for personal use, so adding apps is OK.