So much to see! So many things to play with! So much to learn. When I first got my iTouch and I went to apps store I felt like a child in a candy store. I had to limit my "intake" ($0.99 can add up)and try to stick to the free stuff. I found a nice site that reviews educational apps.
There are many apps that would be useful to students in all the content areas. To name a few: WeDict, Word of the Day, Google Map/Earth, Brainteaser, 6500+Cool Facts, inFactUSA, 3DPanet and the list goes on and on.