I'd have to agree with WiseJD on the reliability of Otterbox Defender and Griffin Survivor and size issue. However, if you are willing to wait, I highly suggest TakTik 360 (click here).
This is not your typical iPhone case. I got it for my 5s and ipod nano. Dropped it in the lake while fishing and survived my last deployment from sand and rugged use. Here's a quick video of what this case is made of and what kind of material used (http://vimeo.com/43643683). It sells for $59.95.
There's a similar one I found - Love Mei (click here).
I think this is the replica version by the chinese. For $49 and availability, I would go for this one.
But my top favorite of all.... Snow Lizard (click here). Everything I am looking for in an iPhone case pretty much sums up this ULTIMATE iPhone case. Just watch the review... nuff said! Hope this helps!