Try RateMyDrawings.com
RateMyDrawings is a website where you can create drawings and have others rate them for you. The interface is a clunky but it's still easy to use. It requires registration to use.
Here's a sample: (It's flash)
http://www.ratemydrawings.com/drawings/landscapes/240202.html
http://www.ratemydrawings.com/
Or you could try ArtPad,
It's similar, but I like the interface better. It's simpler, but it has less features than the one featured at RateMyDrawings .
http://artpad.art.com/artpad/painter/
I know it doesn't count, but try iSketch. It's an online game that has a pretty neat Studio feature. It's like Pictionary, in which you draw and they guess. The Studio feature I mentioned is supposed to be a place where you can draw at your own pace, without a timer or anyone else watching you. It requires Adobe Shockwave.
http://www.isketch.net/