Bitstrips

Bitstrips is an online site that allows you to create your own comic strips. It's simple, fun, and easy. You don't have to sign up for Bitstrips, and it's 100% free.
You can find Blitstrips at http://www.bitstrips.com/

Slimber

Slimber is an awesome site that allows you to draw and paint.  Slimber allows you to save your drawings.  After you save your drawing(s) you can play it back as a video. Slimber is a very cool site. Plus, no registration required!
 You can find Slimber at http://www.slimber.com/

Pixlr

Pixlr is an online image editing software mixed with an online whiteboard/painting-drawing program. You can open a picture from your computer you want to edit, or you can create a new image and paint/draw whatever you want. You can open up an image from Facebook or other places. Pixlr is free and there is no sign up necessary.
You can find Pixlr at http://pixlr.com/editor/