For want of choice of genre, may I suggest you add the usual list of suspects found in most anime sites? You forgot plain humor, after all ( Azumanga Daioh anyone?)
Romance makes up the bulk of my collection, but that's probably because they happen to make up most of the anime decent enough to watch. ALso, as an obsessed fan of realism, romance stories fit the bill most of the time. Imagine: no superpowers, no anime craziness, no action. Sounds about right. But the thing I like the best about this genre is EMOTIONS. To me, emotions play the biggest part in an anime, where the only real "physical" thing are the voices. More later.
Higher up my preference list (and #1 on my must-have list all the time), while covering a wide spectrum, can simply be called, for want of an umbrella term, the weird. Covers pretty much from heavy gore to psychos, ghosts to macabre. Includes Paranoia Agent, SEL, Elfen Lied, and Perfect Blue. Basically, I'm a sucker for anything not normal. Probably since I'm not normal up here in the first place.
Another genre I love is one that almost everyone else loath: slice-of-life genre. Anime like Aria, To Heart (1st season hardly has any romance), Kiki's Delivery Service, and the like. Apart from fitting the bill of my relalism fetish, I also like the laidback attitude these anime usually have. And more often than not, these anime are usually slow-paced and generally calm. In a word, relaxing.
I don't really watch hentai. Not because I'm a goody-two-shoes, but because of the EXTREMELY high unrealistic factor general to this genre. Plus, half, if not most, are not erotic; rather, they are sick. Recently though, I have been catching some hentai for the fun of it (or rather, the lack of anything else to watch, plus the XDCC bots are damn fast). Among the ones that I dump are Love Doll and Cool Devices. And yes, I have watched Bible Black 1st season. Not all it's hyped up to be though, I'm guessing it got its notoriety from the use of Satanism, and the title being Bible Black doesn't help it's cause. No spoilers, but honestly, I'm betting the rituals were inspired by books about Satanism rituals. Pretty much looks like the typical portrayal of small-group satanic worshippers.
Last mention on my list is a pretty small niche. Dunno what's it's called, but for simplicity I'll call it the Tragedy genre. Saikano fits the bill here, which btw is EXTREMELY recommended. There aren't many anime that fits this genre, so I don't really recall any other than Saikano and Grave of the Fireflies. This genre is usually, if not always, coupled with other genre, like romance or war genre.
I think everyone should've noticed by nor that I never mentioned anything about the usual action or humor. That's because to me these are simply cheap thrills, too widespread. It's not that I don't enjoy them, more like I'm indifferent about them, because there's nothing special about them.
Special Section (lol)
Good voice acting make or break an anime most of the time, and in romance anime, bad voice acting is a total disaster. Examples of great voice acting: parting of Van and Hitomi in Escaflowne ending; final outburst of Kaoru against Aoi's father in Ai Yori Aoshi. Bad acting, endless. Any dialogue where the speech is deliberately slow (Kanon's Sayuri) is, to me, unforgivable. High pitched voices are common, but too high and it spoils the show. That's why I never got pass ep2 of Hack Dusk.
Anyway, enough ranting. I need to go on already.