I got a cheapy neoporine case and some generic screen protectors-- only time i scratched the screen was the few times when i took the protector off. The case is good. I think it was like $20 for two cases.
Just curious. I've seen a lot of "best case" type posts in the forum. I originally used cases to protect my older ipods but decided to not get a case to save money (I treat all my gadgets like trash anyways). so far I've been pleasantly surprised at the sturdyness of the ipod touch's structure and glass screen. No scratches anywhere! Although the aluminum back has scratches, but that doens't interfere with anything.
I love using mine without a case. I have lots of small scratches on the back, but none on the screen. I keep it in a pocket that never has anything else in it. I almost dropped it on cement the other day, though, so I'm now considering getting a case.