So you've seen those fancy images sported by Zelda_Pinwheel, Ravenne, Dreams, etc. and you're wondering, "where can I get a unique avatar like that? How come all I have to choose from are these boring cartoon characters?"
Wonder no more. Whether you have artistic skills or are completely without pixel talents, there are tools to help you create that perfect avatar.
Many, many sites can help you if you're interested in creating a cartoon face for your avatar, whether you want it to look like you or completely different. Some will even generate an avatar automatically for you, based on text you enter (e.g. your email address), so you'll have a sort of coded image.
Examples of avatars I've created using these services, for your viewing pleasure, and the websites they came from:

From
http://illustmaker.abi-station.com/index_en.shtml

From
http://www.simpsonsmovie.com/main.html

From
http://www.mrpicassohead.com/

From
http://www.reasonablyclever.com/blockhead/index.htm

From
http://www.miieditor.com/

From
http://digibody.com/avatar-maker/index.php

From
http://www.doppelme.com/

From
http://www.reasonablyclever.com/mm2/index.htm

From
http://turnyournameintoaface.com/

From
http://friedcellcollective.net/monsterid/

From
http://www.faceyourmanga.com/homepage.php?lang=eng
There are many more avatar generation tools out there, including some that use photos as input. Feel free to post more links in this thread!