Well, you might get lucky and find it on ebay cheap, but I use an Otterbox Defender. It's like body armor for your phone. I ran my phone over with a loaded pallet jack and it ripped the rubber covering and dug in and tore a chunk out of the plastic, but left the phone untouched.
I bought the Otterbox Defender a couple of weeks ago for $31 and change from Amazon (retail is $49.99). It really does a great job of protecting my iphone but it does add alot of bulk to it.