If you want something with a bit more bulk and protection, as well as some added grip, the Griffin Survivor is a good option.
Just like with the OtterBox Defender, the Survivor comes with a durable polycarbonate shell to protect against drops and also has a built-in screen protector to protect against scratches and other debris.
It also has rubber flaps on the ports to protect against dirt from getting inside. The outside is lined with silicone to provide a good grip, as well as to absorb any shock from drops.
The Griffin Survivor is just a tad cheaper than OtterBox's offering, priced at just $35.