Odosketch is a neat and free online drawing site that I learned about through EFL Classroom 2.0 (a site I think all ESL/EFL teacher should join).
It’s fun. Unfortunately, you have to register with the site in order to save your drawing, and it doesn’t have the ability to write text in it. I have other free web tools listed in The Best Art Websites For Learning English that don’t have either of those drawbacks.
But Odosketch is still worth a look.