PC Waterproof Shockproof DirtProof Case For iPod Touch 4G Gen4
Got this for the pool on vacation.  I never trusted it enough to completely submerge it but it got very wet a couple of times and I could find no evidence that water got to the iPod.  Made it easy to float in the pool and listen to music and audio-books.  If you want absolute assurance of waterproof, you will probably need to buy the $80 brand.