I have not seen iPod/iPhone cases from Otterbox. I've seen some protective cases from Marware. They looked very similar to the Impact Case from Otterbox. I found that they were on the heavy side as rubber they were made of was thick/compact. It might be a problem or not.
Edit: from the OtterBox spec sheet, the Impact case weight is around 17g or 0.6 oz and it's not made out of rubber but silicon
I've been using an Otterbox since I dropped my first Iphone and had it replaced. It was actually an Apple care tech who recommended it !! Since then, no fewer than 5 friends have bought one after seeing it. It does provide a very good shock proof case which also covers the screen......and I have proven it, believe me !! It fits like a clamshell around the phone, then you stretch rubber over that. They DO make a waterproof version, but have no experience with it. I highly recommend it. They were running a buy one get one sale which I took advantage of for gifts.