Yeah all my sports friends with iphones have the lifeproof cases and I've been jealous ... they add almost no bulk and are top quality.

Seidio Obex is another waterproof case that just came out but looks bulky.

Regardless, my choice to go with the S3 was largely based on these types of accessories becoming available. That's previously been one of the benefits of the iphones, lots of quality accessories due to volume of sales.