I never really thought about implementing an idea like this but thankfully, Speedo and iRiver have already done the hard work for us. The Aquabeat Waterproof MP3 player has both an appropriate name and look. It can go up to three meters underwater and has a mind-blowing 1GB of storage. Then again, how much music are you gonna need underwater?
With everything being waterproof, I tried to think of how you could possibly use this thing while swimming in the ocean. Then it hit me that this is the perfect MP3 player for your boat or jet ski unless you have an Otter Box or something similar. Oh, and it floats like a turd in case you lose it. Seems like a sure win for $145.