I originally had the clear hard case that you can buy from the apple store, but it bulked the phone too much.
I went with a BSE (Best Skins Ever) skin. I love it. Kinda has a tackiness on the back while the screen sheet is smooth enough where it feels like satin. Cant tell its there unless you're looking for it.
i've been through several. the agent18 case is by far the best in my opinion. I use that and the belkin sport armband. Soft cases leave room for dirt to scratch up the iphone the agent18 doesnt and adds very little size. Hope this helps
I had an ipod touch that I had a leather flip case for it. It added kinda to much bulk, it defeated the purpose of it being a slim device. And the screen is already nearly scratch resistant so unless you drop stuff frequently then I think a case is kinda useless. So when I sold my touch and got an iphone I never bothered to get a case for it.
the one I had was made by griffin if you wanted to know.