First I have to talk about Order of the Stick. Its a 3.5 D&D webcomic that is very well done. Its not just some verbose garbage cobbled together with some pictures. Its done by a guy who is a real deal creative writer and skilled adventure writer.
All of the stock avatars are done in the style of the webcomic, which is a simple one to mimic. Therefore, the convention on the OOTS forums is to take a character you like, from anywhere, and draw them in OOTS style. My avatar on those forums is "The Monarch." I also did a basic monarch henchman, 2 of William Murderface, and started on an Awesome-X.
I also made one of Bruff from a show here on the escapist called Doraleous and Associates. Eventually I broke down and registered on the forums here, so it was a no brainer to use OOTS Bruff as my avatar. I made them with inkscape.