Well, aside from Get Backers, in anime I used to be really into Yu Yu Hakusho and Ruroni Kenshin, and I'm currently rather taken with One Piece. Oh, also Petshop of Horrors for awhile a couple of years back, and Gensomaden Saiyuki (I thbelieve that's the proper title, everyone just tends to call it Saiyuki)
As far as books go, I was into Harry Potter for a while, but the fandom for that is sort of insane. There's also Dresden Files and whatever I can find of Codex Alera, which are two series by Jim Butcher that are really good if you like fantasy and humor. Also Discworld, by Terry Pratchett, which is fantastic even if you don't like fantasy. Oh, and the Jeeves and Wooster series by P. G. Wodehouse, and Sherlock Holmes.
For TV/movies, I like Star Trek TOS (that's the original series, for you non-Trekkies) and the reboot movie, but I've never seen the other series. Also Supernatural, though I've been less and less interested lately.
I have a tendency to get into fandoms for a short while right after I read a new book or watch a new movie or series, but these are the fandoms I've been in for longer periods of time. Actually, there's fewer than I thought. Maybe I'm not so bad as I thought