When I first got my iPod Touch, I got the Black Speck ToughSkin Case.
It looks like this:
Overall it's a pretty good case and very durable too, but I found it too large and cumbersome. The iPod is 8mm deep, and the case is 2/5 of an inch. That's adding 27% to it's chubbiness, which seems like a lot to me.
Shortly after, I dropped my iPod in a toilet for about a second. It stopped working for a while but the only lasting damage was to the internal speaker. Just thought I'd let you know...
I now only use my case when I really need it to be protected. (Like rock climbing.)