A great game that might hold your attention for a while is Rappelz. It's a fantasy MMO with a good amount of variety. One thing the game focuses on is pets. Every single character in the game can have pets, and there are even pet classes which focus on pets. It's a fun game that had me entertained for quite a while. It's very time consuming though.
Another game that held my attention for quite some time is Sword of the New World, which is similar to Knights of the Old Republic in the sense that you control multiple characters at one time. It's an extremely in depth game with LOTS of playable characters. You start out with only five (or six, I can't remember), but you can unlock character cards by completing quests for certain NPCs, which then let you create a character of that same NPC. The NPCs usually have some great skills and stances that the normal five characters don't have. It's very fun, and I highly recommend it for RPGers. Another time consuming game, but probably not as much as Rappelz.
Another great game is Flyff. Stupid name, great game. It's like a Korean version of WoW, but even more time consuming.
Speaking of WoW, you can legally play private servers for free. Just download the WoW tutorials and patch up the realmlist.wtf (that's the file extension!) and you're good to go! A great website with lots of private servers can be found here. I personally liked the WoWgasm server because it has a lot of awesome custom content and allows you to level up to level 254, but if you're more into blizzard style play, you can try the WoWscape server.
If you like Star Wars, you can play the non-crap version of Star Wars Galaxies free with the Star Wars Galaxies Emulation Project. I'm pretty sure, although not positive, that you can download the game through the Launchpad Enhanced app. It has some pretty neat features like server status, automatic updates, links to related websites, launching the game, and being able to run multiple clients at once Unfortunately, the emulation it is still in alpha/beta stage because these guys are reverse engineering the entire game. I was addicted to this game (the retail version) for about four years, playing it 10+ hours a day. This game is totally awesome. I can't wait until the Emulation project is completed!
If you don't like any of these games, you can check out mmorpg.com. They have a neat game list with a LOT of MMOs, including upcoming titles. I really like this list because it has great sorting features, they provide details on all the games, include forums, player ratings, etc. It's a great site to check out if you're bored.