About the only good thing about a waterbed is its temperature regulation. With the ChiliBed mattress (invented by the nephew of the guy who dreamed up the waterbed), you get the best of both conventional mattresses and waterbeds, giving you sophisticated temperature control without feeling like you're floating on a life raft.
If you sleep with someone who always feels chilled but somehow emits heat like a June bride in a feather bed, this two-zone water-cooled contraption is for you. It keeps the cool side hot and the hot side cool, and its environmentally friendly 100% soy composition keeps even the treehuggers happy.
Don't need a new mattress? There's a ChiliPad, too, that does about the same thing, sitting on top of your existing mattress.