I've been splitting time between Rift and Neverwinter.
I played Rift at launch, but quit before the end of my first month... I couldn't remember why I quit and decided to give it another shot. I'm really enjoying the game... I realize it's probably been said a billion times, but it does remind me of WoW in its glory days and i'm not a big "raid" guy. WoW still has more charm and humor, but Rift makes up for that in neat features (i.e. events/rifts and the awesome class system to name a few). Right now you can play the first 20 levels for free and you can also earn free game time through some social gaming program called Raptr. I signed up, but not completely sure how it works. I know I haven't qualified for the free game time yet, but it looks like I will once I get enough hours of Rift under my belt.
Neverwinter has been a great substitute MMO for me. You don't have to worry about a monthly fee, the game play is pretty fun, and you can get a good amount done in an hour. So if I only have a short amount of time to kill, I boot up Neverwinter and knock out a few quests or a dungeon. I have not felt the need to put money into the game... I may end up doing so anyways, but it definitely is not required. There's a good Wine port of Neverwinter on the Porting Team website, so being able to play in OSX definitely helps when I need a quick game.