"Comics" is a problematic category; technically, it describes a format, but I've seen it used to refer only to DC/Marvel fandom.

Biggest comics fandom I can think of outside of those is Elfquest. There are also small indie-comic fandoms like Cerebus and Flaming Carrot. And if Chick Tracts have a fandom, I suppose it counts as comics fandom. (There are parody tracts.)