Just sticking to Buffy, Buffy/Spike. Duh. Willow/Oz. Not that I have anything against Big Gay Willow, but going back to the early seasons, I did like the cuteness and wolfy angst of that pairing.
2. Favorite non-canon pairings?
Um...yeah. Xander/Spike. With an up-and-comer of Angel/Spike. And a few dark horses: Wes/Angel, Wes/Gunn. (Hmm, notice that no one writes Angel/Gunn. It's not a Gunn thing, I suspect, because people do slash him with Wes. I guess it's a chemistry thing. I mean, there's a big black box of mysterious nothing for you: the relationship between Gunn and Angel.)
3. Favorite obscure pairings?
See, everyone who reads my LJ surely knows these things, which makes this meme a bit boring. And one must note that some of these are mostly in my head, but: Riley/Spike. Um. Hmm. I thought I had more.
4. Pairing you won't read no matter how well written?
Things with Synder and Giles, which I find squicky. I've skimmed a few Dawn/Buffy stories, just with the drive-by rubbernecking instinct; these particular ones--don't remember what they were--didn't happen to squick me per se, I just have no interest and don't see the point. I've read a lot of one-off obscure pairings, some of which work (Xander/Larry), some of which don't so much (Cordy/Lilah).
5. Pairing you used to dislike, but grew to like or vice-versa?
I used to dislike Spike/Angel, because of how people wrote Angel (smug, condescending, mean and bullying without any real tenderness or affection). I'm seeing better stuff now.
6. Does it matter to you if your pairings ever get recognition by TPTB?
Only in that I sometimes mourn the lack of canonical m/m relationships, and whimper for what might have been. It was my fantasy that in the second half of S7 they'd diverge for an episode from the dark arc and get in one last AU, a la the Wishverse. I'd have loved to have seen some S/X snogging. It was, okay, a hopeless fantasy, but it sustained me.
6b. If they already have it, does that make the pairing seem more legitimate somehow?
A little recognition never hurts. But what does that even mean? I see deliberately embedded S/X slashiness in the show. Not sure if that's what recognition means. In that sense of the word, recognition is what helps build a viable ship.