In general terms:
Battlestar Galactica (the new one, although also like the old one), Forever Knight, Star Trek, anything that has Vampires in it... and it is pretty obvious I wouldn't be here if I didn't enjoy L&C.
I used to be involved in a Buffy/Angel AU fandom.... but it got stale.... and died (kinda funny really).
I don't do the fanfic thing much with the other shows though. I want BSG to finish before I venture into fanfic there or I'll get disappointed, I have and am still reading a few Forever Knight fics, and I don't bother with ST these days as there is more badfic on the internet than anything in my experience of it. I prefer to read those authors who've actually been published in the Trek universe...
Having said that, I prefer to read original fic these days outside of L&C... I like seeing how creative people can be.