Well, I was able to put this picture on PikiGeek.com for a sweet contest thing and I've sold a few on Etsy, and I just realized I hadn't put it here yet! I am an airhead.
Anyway, the poster is in alphabetical order starting at the top of the head, and it's got characters from video games, movies, and cartoon shows! I spent several months working on it and it's developed into a real labor of love.
I still have a few copies left of the poster that I'm selling here, in case anyone wants a copy: [link]
And if you ever get stumped trying to name all the characters, here's the list in the order they appear, in spreadsheet form: [link]
You may call it obsessive, I just call it organized