(The iPod case I got for my first iPod was perfect for it, but the new iPods are so much smaller that they just swim in there. Also, the holes don't match up.)
There were several cool cases to choose from for the 5G iPod at the store, including a great Superman one that I absolutely would've gotten if it had a belt clip! A Google search reveals the same company also has a Batman and a Homer Simpson version, among others. Using the touch-sensitive wheel through the case wouldn't bother me; I've already done a bit of that with my slip-cover. Yes, it can somehow tell when my finger is moving along outside to change the volume, not just pushing on one of the pushable bits.
But while I could have managed without a belt clip, and I have been for months, that was one of the points of getting a new case. Slipping the iPod in and out of pockets was among the inconveniences. So, no Superman case for me. There was also a nice case that I almost bought that entirely covers and encloses the iPod so it's not obvious it's an iPod. That's probably a good idea for carrying and long stretches of listening without needing to interface with the iPod, but again, controlling the thing (or watching video, for that matter) would require slipping the iPod in and out of the case. So, no.
The case I finally picked was the ToughSkin from Speck, a rugged, black, rubber case with a clear, plastic screen protector and holes for the headphone jack, hold switch, control wheel, and dock connector. Basically, the iPod will never have to come out of the case! Perfect for my needs. It also has a modular belt clip that it can slip onto, very similar to the one that came with my old, denim (!) iPod case and a couple of handheld two-way radios I've been using. I haven't checked yet to see if it's the same size attachment, which would be convenient.
The only big drawback I can see to this case is that you can't tell I chose a white iPod instead of a black one!