Check out this site- Sketch Swap. You sketch something, hit submit and then you get to see someone else's sketch manifest line by line as they drew it. It's neat to see what some people can do with basic brown lines.
And here's one that lets you use different colors: Scribbler.
I took some screen grabs BUT they save in .tiff format and I have no clue how to change them to .jpg at the moment. Go sketch something and you'll see what I mean.