GSI Cool Sealed Waterproof Adjustable Armband Bag for Underwater Swimming/Sports/Surfing/Skiing/Fishing, Protects Apple iPod Nano and Most MP3/MP4 Players - Includes Custom Waterproof Quality Earphones
I had real doubts as to whether or not this would work, but it was such a good price I had to take the chance.  But it does work. I've swam for 30 to 45 minutes at a time several dozen times and it's never leaked into the unit at all.         There are only 2 drawbacks I can think of:  (1) the headphones are not the best quality and of course you can't substitute in other headphones b/c the wire is integrated into the unit as a whole as a part of making the thing waterproof (the part of the unit from which 