Toilet Lid Sink
If you live in a desert area like we do, you can already tell why this Toilet Lid Sink is a good idea. The water used to wash your hands is recycled to flush the toilet.
On another note, it saves space in your bathroom. If you live in a postage-stamp apartment or house, the room saved by having the sink and toilet be a single unit is enough to fit a full size tub instead of just a shower unit.
I would like to see a more elaborate version of this that has a stopper, slightly deeper sink and both hot and cold water so it can completely replace the sink in my bathroom.