I just ordered a silicon case from Amazon for a penny plus $2.98 shipping since I had some store credit there. It's a fairly generic-looking silicon case, but since the other colors like it were over a dollar, I figured they were having a hard time unloading the purple ones. A girl's gotta catch a break when she can.
I'm really waiting for a soft-hard hybrid case for impact absorption and prevention of dents in the corners. I too would love the Speck Candyshell for this phone, but I can't imagine putting that case on, with the way the Captivate is shaped. I could see something like the Switcheasy Rebel, with a rigid spine that snaps over the softer, form-fitted case. The Amzer looks most promising, with what looks to be raised corners, but I'll probably stick with what I just bought until I see something that catches my eye.