There are three potential hits coming out soon:
Star Wars the Old Republic, which I don't think I care enough about to bother with, but the story potential sounds like it's going to be a big hit. I guess it depends a lot on how many light sabers are going to be swinging around. Something about Star Wars has always been fun to watch, but I never got into the extending universe of comics, books, and video games.
Rift...Sounds like Trion is producing a well-polished game in the manner of Blizzard. This one I might give a shot, just to do something not related to WoW.
Guild Wars 2...I didn't play the original Guild Wars. But now that I know that the game is sort of like Hellgate: London in that you have a public hub and a bunch of instanced dungeons, I might give the sequal a shot. It's not really my preferred method of play, I like to see other players running around in my game worlds, but I enjoyed the hub experience in Hellgate: London and if Guild Wars is perfecting that style of MMO, there's no reason for me not to give it a shot.
I won't be playing more than two games at a time, but that doesn't mean I can't eventually own them all and just jump in and out of them every other month or so.
Anyway, I've been exclusive to WoW since Tabula Rasa and Hellgate: London both shut down, so I'd like to give something else a chance.