CIMO ShockProof Case
If you're looking for something really rugged, but maybe not as bulky as the Otterbox consider this case from CIMO. It's part of their shockproof series, so it's very durable.
The CIMO shockproof case is basically the same dual-layer design as most other cases. The inside is lined with TPU for shock absorption, and on parts of the outside, then the rest is a hard polycarbonate plastic.
You'll get plenty of protection thanks to raised edges around the camera, and another raised lip near the screen. Making sure the phone doesn't touch a table when you set it down, to prevent damage or scratches. It's a decent little case, and you can choose from a few different accent colors.