I just bought a Speck Toughskin, which I really like. It feels pretty rugged and seems like it would protect the iPod if I dropped it (I'm a klutz). It has a detachable belt clip on the back. I also like the hard screen protector--it has a little rubber rim on the bottom so it doesn't actually touch the screen, which should keep it from getting scratched. My only concern is how well the iPod will dissipate heat while charging, but I figure I can punch a few small holes in the back if it becomes an issue.
The only downsides to this particular case are that you cannot put it in a dock, it does bulk up the iPod a bit, and it completely covers the iPod so it's not the best choice for someone that wants to maintain the standard appearance of their iPod. But for good solid protection, it seems pretty hard to beat (no pun intended).