I just got my Lifeproof case for my iphone 4.
Its a fully sealed case rated to IP68, and can be fully submerged in water upto 2 meters.
Its also shock and dust proof.
If you drop your phone a lot, especially down the toilet or live on the beach, this case is great.
Also available for the Iphone 3gs and ipad.
Here's a pic of mine submerged