This is SO my topic!
I have both an otterbox and an H2O audio. I have the otterbox for my nano, I use it to walk in the beach, i take it to the pool but it is only good to about 3ft. They do stand behind it 100% and will fix your ipod if there is a leak as will H2O audio. I have used ithe otterbox in the water but sometimes the pressure of the water can change the volume which is very annoying.
I bought a used shuffle from apple (referb) for $40 the H2O for the shuffle and the head phones. You have to use the H2O headphones with it BTW. and the case was the best price on the H2O audio website.
So here is the deal. I love to swim with the music. I like the H2O it fits well on the armband that it comes with the shuffle is great for swimming because you load your favorites and they just , well shuffle. The downside is the headphone. they work ok, the sound is not fabulous and you can't stop water from going in and out of your ears. You also might like to have a cap on the keep the headphones in place.
BUT i can't stand swimming without music
cuse there is nothing worse than being in my own head for an hour!
waterproof mp3 cases for swimming?
it. I think I got it online at Newegg, and it was about $40. I do water aerobics in my backyard pool and this has helped me increase my workouts from a boring 15 minutes to sometimes an hour. I have had NO problems with it. 
