WoW is the MMO equivalent of dope. Everybody seems to do it, nobody seems to notice the harm, and long-term use makes you essentially dead on the inside.
Wrong. That's Everquest.
DDO: Boring, very hard to play solo. I tried it for awhile and am sad to say I spent some money on it. I'm not going back.
Agree. Not just this, but the endgame content is so bad that Turbine actually made a positive feature out of starting over at level 1.
Age of Conan
Haven't heard much, but what I have heard is positive. It could very well be a worthwhile game to play for a few months, and if you get bored then maybe your appetite for more WoW will come back.
Everquest I/II
The original Everquest had a large following in it's day, but that's just because it had the best marketing IMO. Both I and II are terrible.
Guild Wars
Guild Wars is like a f2p Everquest with more PvP. I played this for a while, and my opinion is that you get what you pay for.
Lord of the Rings Online
After the movies, I wouldn't bet on this. The franchise has been whored out since the penning of any and all books after The Hobbit.
Rift
Haven't heard anything about this at all.
Star Trek Online
Funny story. I saw this on the store shelf at my local GameStop, and the guy behind the counter all but refused to sell it to me on the basis that it was that bad.
Star Wars: The Old Republic, and Warhammer 40k: Dark Millennium Online.
I think SW:ToR is going to be better in your situation given that it's going to have more of a stylistic difference from WoW than 40K does.
My suggestion: Ultima Online. The demo has 100% free digital distribution and 14 days of gameplay. You'll get all but the latest expansion for free doing that as well (and the latest expansion is just $20).
Another thing that might be worth wasting a couple months on is SMT:Imagine, but I'm not a fan of developers like Aeria Games and GPotato. I feel the companies emphasize quantity over quality. As in, your SMT:Imagine account will also get you access to about a dozen other grindy MMOs, just like SMT:Imagine.