You can find small sinks that are manufactured for boats - my mother was on a similar search and this seemed to be the way to go.

The Porcher Elfe Wall-Mounted Hand Basin Sink is 19-1/2'' x 9-1/4'' (so it sticks out from the wall just over 9 inches). The faucet is mounted to the side, so it keeps the sink very flush to the wall. It is available online for about $200 (plus/minus 15 dollars, likely nets out with shipping).

http://www.porcher-us.com/ProductNew.asp?prodID=790

Don't forget that they make corner sinks.

Don't worry, there are some options out there.

Here's a corner mounted one:

http://www.designerhomegallery.com/american-standard-14.html

And here's a regular wall-mounted option:

http://www.signaturehardware.com/product673?utm_medium=shoppingengine&utm_source=nextag

Not sure what your budget is but Duravit has also got some very nice small sinks.

Look for sinks for traditionally small spaces such as bar sinks or sinks for trailers.

try lacava.com
http://www.lacava.com/Images/sinks/5088-2-big.gif
aquababy

you might want to try this sink:
http://pathtofreedom.com/peddlerswagon/homestead/ecogoods/toiletlidsink.shtml

It uses the water you use to wash hands to fill the reservoir of your toilet. So if you're just looking for something to wash hands in after you use the potty, then this would take up no extra room. And use less total water.

I also installed the Porcher Elfe in my teeeny weeny guest bathroom. It looks great and works well for hand rinsing. I purchased mine through Home Depot on 23rd Street (which I might add, had an extremely helpful staff).

I would also recommend a trip to Gracious Homes on the Upper East Side where we later found a whole series of small sinks displayed.

You can find the world's tiniest sink in my bathroom. I'm fairly sure the landlord bought everything from Home Depot or Lowes.

Try Bellacor, I have bathroom that is 4x4... under the stairs.
Here is the link

http://www.bellacor.com/results.cfm?Cat=107&Page=1

take a look at www.decorplanet.com some funky stuff.

The toilet-top sink is what the Japanese use in their WCs. Readily available online.

Duravit, designed by Philippe Starck model #076138000, only 15" across. Super cool, and cute.

Find a ceramic bowl you like, have a hole drilled in it for the drainage. by plumbing parts and assemble.