Doodlewall is a simple Flash site that allows you to create an account and then create your own sharable wall to draw on. A URL will be generated and that will be where your wall will be located. It can be private or free.
Doodlebug is filled with content. You do have to register here.
Slimber allows you to create your drawing and it plays it back to you as a video.
Online Sketchpad is a very simple drawing pad
Doodlebuddy is loads of fun! This free App is a must for your Ipad
Draw For Ipad is a simple line doodle app that is easy to use and free. Ipad
Adobe Ideas is your free digital sketchbook on the Ipad