Create an avatar or cartoon image.
Build Your Wild Self - A great site for the younger kids to create a digital version of themselves with body parts from other animals complete with sound effects. This would be an awesome addition to one of the voice sites. Lots of fun and easy to use!
DoppelMe - Easy to use avatar generator. Everything is free to use! Registration is optional, but doing so gives access to additional features for your avatar.
FaceYourManga - The World's Leading Avatar Generator. Create yourself, celebrities, anyone using this simple tool!
Hero Factory - Piece together the super-hero version of yourself and print a comic book cover generated by the Web site.
Meez - A site for the older kids. Registration is required. Once registered, you are given "coins" to help customize your character. Additional coins can be purchased, but you are given enough to have fun with initially.
SP Studio - Create cartoon look-a-likes in the style of South Park. A lot of fun options here!