We have been showing toilets with sinks built into the lids of the tanks for years, including home-made and aftermarket plastic versions. Now Caroma gives us a dual flush toilet that they claim will save a family of four 30,000 gallons of water per year over an older toilet.
The dual flush controls are detailed neatly into the lid. More at Caroma
More, but less elegant, toilet tank sinks:
Wash Your Hands With Toilet Water
Sinkpositive: Save Water, Wash Your Hands
Hack Your Toilet and Save Water