Paintschainer attempts to intelligently colorize artwork that you upload. It's very good at tight line art (such as the flowery anime portraits provided as samples) and can color them in several different styles, but the results get abtract and "computery" when it has to deal with loose pencils and shading.
I sketched a little cartoon pirate and it did OK, but seems to have some trouble distinguishing "objects" to colorize
Here's what it made of a cut-through sketch of a hollow tree:
I like it! It turned it into a weird blob of living flesh.
This abstract landscape sketch of mine came out like a psychedelic watercolor: