I've had the parts to put together a "mini" (~300mm) hexacopter for a while now. After firing up the trusty ol' 3d printer, a few hours later I had this sucker.
Common credit-card style card for scale. It comes out to about 18 inches long, and 8 inches wide. This design is pretty obscure and unique. Two rotors point down, two up, and the rear two rotors form a V-shape, giving the frame it's name. I don't expect it to be particularly efficient, but it should be pretty cool!