Well.. there are tons of fun ones. I really enjoyed 9 Dragons, a china kung fu MMORPG. Takes forever to level up though, it's a true grinding experience. I've tried The Old Republic as well but it just feels like a total wow clone... In addition to that I've played many other fun ones.
Do you know what MMORPG has been my favorite ever since I started and stopped playing it? World of Warcraft. It's just a fantastic game! It has the best content scaling I have ever seen... if you are a casual gamer you can simply enjoy the leveling and the community, and maybe if you are up for a bigger challenge do some 5 man dungeons or join a battleground.
If you are looking for a challenge, like me and so many others you can do some 2v2 arena's, or do a raid. Killing Lich King on 25 man heroic, or reaching 2000 Mixed Matchmaking Rating in 2's has been one of the most satisfying moments of my gaming life.
WoW has absolutely done it right. They nailed what a good MMORPG should have. That's why so many millions of people are willing to pay monthly for it. And that is why thousands more play WoW on private servers.
WoW is so good I seriously considered it's influence on my time management in life... Ultimately, I quit world of warcraft as I recognized it was wasting too much of my time. The memories are still there however!
If you have time and patience for a good MMORPG... I hope the above has convinced you ;)