I have the CaseMate POP case, it does not seem to add too much bulk, but still provides more than adequate protection. Very happy with the case.
The case snaps on. It's a combination of composite and rubber on the outside, the inside is lined with silicone for shock absorption. The edges of the case are raised in case you drop the phone flat on its face.
It comes in a two-tone scheme. I have the white/cool grey. There are a bunch of other colors avail. The CaseMate website lists it for $30+, but I bought it on Amazon for $21, incl. shipping.