I bought the casemate (cm) one from AT&T when I picked up the phone, at the time it was the only one out so far. I've been really happy with it.
It's a two-part case (soft silicone, hard plastic) that's tightly fitting and unobtrusive. I actually just chipped it this week finally, one corner of the hard case is missing but it doesn't really effect it. I'm actually not sure how it happened, lol, I've dropped this things at least ten times from height in the past year and a half and it never broke. Importantly, the inner rubber lining comes out on top, kinda embedding the screen a bit so if it drops on its face the screen doesn't touch asphault/whatever (also helps you get a grip).
Anyway, they're $25 from casemate, I'm sure you could pick one up cheaper somewhere. Well worth the money.
---------- Post added at 11:09 AM ---------- Previous post was at 10:48 AM ----------
Amazon has them for $8.01. Deal!