Who doesn't need a Cylon from Battlestar Galactica toilet paper dispenser? What about a taxidermied mouse USB drive? Fart-operated TV remote, anyone?
Check out Gadgetbox's 10 Completely Useless Homemade Machines.
You also might enjoy this clip of what's been dubbed the world's most useless machine. I kind of love it. There, I said it.
[youtube=http://www.youtube.com/watch?v=UmQ5LsNMXZ4&feature=player_embedded]