This one is pretty basic and nice for just jotting down notes and quick things.
StickDraw – Animation Maker
Make your doodles MOVE! Add animation to your own scribbly stick figures with this sketch and play app. Additional plugins are available to add more features.
Magic Doodle 1.5
For serious scribblers, this is definitely the app that can give you the most professional looking results. Also comes in a pro version with more palettes and brushes.
Draw and Share (painting app)
Use brushes to paint with your fingers, and the text tools and clip art to create some crazy stuff to save and share with your friends!