http://www.kk.org/cooltools/archives/001184.php
Homestead
Toilet Lid Sink
A Sink in the Top of your Toilet
You already know why it's good!
-- Jeff Hoover
[After you flush the toilet, incoming water cycles up through the sink before going down to refill the toilet tank. Water is used twice: Once for hand washing, and a second time for the next flush. -- CP]
Toilet Lid Sink
$89
Available from Real Goods
Manufacturer not listed.
Seems like it would be a good thing for airplanes, to save space or something.