Not much of an MMO person myself, but I think that a good "supplement" MMO for you would be free to play or buy to play (as you're already spending a lot on subbing for SWTOR), and maybe fantasy instead of sci-fi. I played Guild Wars 2 quite a bit (quit eventually as I didn't like the setting, story or characters) and it's a pretty decent game. You could maybe try Neverwinter, which is f2p and seems like it has a better setting than GW2. Elder Scrolls Online will be out on April 4 but it will be a sub game (seems very good though). I've heard that The Secret World is a pretty good MMO in terms of story and setting, and it apparently has very interesting questing.
I've looked up on the secret world once or twice, and the modern-fantasy element if the game doesn't pique my interest. Also, Funcom's making the new(and really, really bad-looking) LEGO MMO, which makes me question how qualified of a developer they are.