As others have posted, there aren't any waterproof ipods although there are theoretical cases to waterproof an ipod -- but of course the buds would also have to be waterproof.
I wouldn't opt for a waterproof case for an ipod. I read an article awhile ago and as I recall they recommended self contained mp3 players that fit basically around the ear so one doesn't have wires leading from the player to the ear buds -- since it is going to be used for one purpose, it doesn't have to have an enormous capacity since one can do workout playlists.
Some days I pray for Silence, Some days I pray for Soul,
Some days I just pray to the God of Sex and Drums and Rock 'N' Roll.