I actually can't identify most of the characters, since I read a limited number of webcomics, but these are the ones I was able to pick out:
- Gabe from Penny Arcade
- Joyce from It's Walky!
- Anders and Maria from Anders Loves Maria
- Stick figure guy from xkcd
- Annie from Gunnerkrigg Court
- Choo-Choo Bear from Something Positive
- Lucy from Bittersweet Candy Bowl
- Pintsize from Questionable Content [?]
- Skull from PvP
- Zii from Ménage à 3 [?]
- Biff from Biff
- Clango from Diesel Sweeties
- Boo from Megatokyo [?]
- Philippe from Achewood
- Gastro from GastroPhobia
- Rodney from Raven's Dojo
- Dromiceiomimus from Dinosaur Comics
- Slick from Sinfest [?]
There's a couple other characters which seem familiar but I can't place, and a couple others whose identities I have thoughts on but can't be certain of.
So, why not make your own guesses here? I might learn a few things, maybe even add a new webcomic or two to read.