I bought
the black and red case from the Sprint store that's already been mentioned a few times. I wasn't super excited about the red but the other clip on case was the chrome/black one from Body Glove that looked cheap and picked up fingerprints immediately, making it look pretty gross.
Thus far I'm pleased with it, it feels sturdy and the slight rubberized grip makes it easier to hold the phone while taking photos (without the case I always felt like the Epic was going to slip out of my hands when taking photos). All of the buttons are easily accessible and the camera/flash are nicely recessed and protected but not obscured.
I'm hoping that the new Seido cases will be a bit thinner to reduce pocket bulk and maybe even allow use of the home dock without having to take the case off. I'll likely try one of those once they're released.