I'll also second the gay/lesbian genre. I've been poking through the listings and it looks like the number of comics we have that feature gay/lesbian/other sexual preference themes has grown and they're not all yaoi and yuri. Some of them fit in other categories, but most seem to be otherwise. Might have to come up with a better name than gay/lesian/other sexual preference though.
Third on the GLBT category. I mean, a romance comic is a romance comic, whether it's yuri or yaoi or whatever. But what about comics that focus more on the GLBT experience/ lifestyle instead of the sex/romance? They're a little bit different than "slice of life" because they have dealing with sexuality/gender/etc. as their conceptual axis. I think it's a significant enough "niche" that it deserves its own category.