Whatever reason(s) you may have, these tools could surely help you out in making a cartoon or anime version of your self.
#1 - Anime Face Maker 2 by Gen8 (http://gen8.deviantart.com/art/Anime-Face-Maker-2-182829244)
This is my personal favorite and I usually spend a lot of time playing with this tool. If you are an anime otaku, you will surely get hooked to this app. Its very addicting. Its plain awesomeness I can't say more. XD
Apologies for the exaggerated review above. While its true that this application screams cuteness and has a very friendly interface, it isn't exactly perfect. While using it, you can say it was created for gaming/entertainment purposes since there is no option to save and download the generated avatar through the application. You have to do a manual print screen + paint + paste + crop combo or use screenshot tools in order to get your avatar. Or we can say the creator was just being lazy. XD
# 2 - South Park Studios (http://www.southparkstudios.com/avatar)
Fans of this American animated sitcom will surely love this app. I found another site to create your own South Park character but I preferred this one since the interface is better and the range of preferences and accessories is greater.
To be honest, I haven't had time to watch any episode but I truly love the cool character design. Also, my crush from college loves this show so I'm confident that this is good. <3
# 3 - I Am Bored Avatar Maker (http://www.i-am-bored.com/bored_link.cfm?link_id=9962)
This website on the surface is a forum for geeks but also hosts various applications including the avatar generator.
The tool has a very simple interface but the character design options are very fun.
# 4 - Face Your Manga (http://www.faceyourmanga.com/)
I believe that this is a very popular avatar generator for wherever I go online either on Facebook, Twitter, Pinterest, blogs or forums, there seems to always be a user with a profile picture created through this app.
What makes it a hit (imho) is that its the tool that you can create a cartoon which is closest to a persons physical features. The output will literally look like you given that you have carefully selected the appropriate features.
When using this application and you want the result to be identical with your self, it's best to get a picture of you handy so you can use it as a guide. But of course, you don't really have to do that. Just create whatever would make you happier.
And a little bit of trivia, their avatars are called "Mangatars".
# 5 - StorTroopers.com (http://www.stortroopers.com/) - This application is no longer available.
I don't think this would appeal to most people, but I like the 8-bit-ish/old fashion computer graphic/pixelated design. I can't find the best words to describe it so I guess it is better to check it for your self and see if it suits your discriminating taste. :D
The application runs in Java and could take a few moments to load.