I've got a Samsung Solid Extreme. It's a basic, no-frills, phone, but so far has taken a proper beating and carried on working just fine. A friend of mine who's a mountain bike skills instructor has the same phone and swears by it. Decent battery life, makes and receives phone calls, not insanely expensive.
I've not used anything else similar, but it seems to do what it claims and means my iPhone is safe and dry at home.
Your other option, obviously, is some sort of of toughened/waterproof case.
Edited: 15/06/2012 at 13:09