I'm surprised nobody has mentioned Goon yet. I mean, this cartoon character was definitely one of Dave's favorites pastimes when I knew him, and for me was an extension of his personality, both happy and fun.
Who was Goon? I don't have any pictures (maybe Kevin or Don do?), and I certainly don't have enough skill to draw him (yeah, I suck that bad), but he was this green cucumber shaped alien with yellow lips, who was always the source of some bizarre antics in comic strips coming from Kevin or Dave. Goon had a song ("doopy-doopy-doopy doo, doopy-doopy-doopy doo!" - got a link for that one?) and even hosted a web site for a short time.
Thanks for Goon, Dave!
Update by Kevin:
Here's a (old and therefore really bad) recording of Goon's theme song, written by Dave and myself: Goon's Circus