I'm not sure that I've captured every sketch that has surfaced, but here's a quick list (20):
Lynch* Mutts
* Play-Dumb #1
* Play-Dumb #2
Engstrom* Grazin' Bran
* Cap'n Crud
* Hurtz
* Dull
* Pupsi (artist's return card)
Wheaton* Quacker Oats #1
* Crust #1
* Crust #2
* Crust #3
* Crust #4
* Gloom
* Ultrabite
* Creep #1
* Kentucky Fried Fingers
* Wormy Packages #1
* Ajerx (artist's return card)
Zapata Bros.* Band-Ache
I've got pics of 17 so far (all from ebay I think, plus the one Rob pulled), but I'm a week behind on ebay checking. I'll try to snag the more recent ones tonight.