This video shows several different options for creating your own avatars online.
General Avatars:
http://www.faceyourmanga.com
http://avatars.yahoo.com
http://www.doppelme.com
http://www.planetcreation.co.uk/createpic
Specialty Avatars:
http://www.sp-studio.de
http://www.rabbids.com/YouAsARabbid
http://www.simpsonizeme.com
http://www.makewee.com