I plan on getting an Xbox 360 around christmas because my friend, Becky, is getting one for Halo 3. So I'll get that as well. What I'm wondering is, are there any good online-multiplayer rpgs?
 

There is one MMO tye rpg for the 360, and that is Phantasy Star Universe. Its good if you like Dungeon Romps, and it has a really devoted fan base. The only down side is that you have to pay an additional fee to play it.

FFXI is also available on the 360 so you could give that a try. 

Hey man, I have a 360 to and have had it for about a year. I played halo 3 and gear's constantly. Right now I am trying to think of an online  mmorpg that is on the xbox 360 for you...as far as a I know most of the Online games with live are First person shooter games. What weirdly springs to mind is Oblivion and such but there definitley not online I think. Sorry man. This medium sized post hasnt helped you at all xD

Age of Conan was supposed to be released on the 360. Might not happen now tho considering they lost most of their players...

They are saying that Age of Conan will be released for 360, but not for a while. I think they are trying to incorporate the PC servers, so its all one big world. That might take some time, but it will be worth it IMO. The only 2 actual MMO games for the 360 are FFXI and Phantasy Star Universe. FFXI has the same servers as the other two systems, so its a bigger community (if people still play it). But Phantasy Star Universe has a flowing feel to the game. Its a game I like to play when I just want to kill things and talk with my buddies.

The only difference between the two are the amount of people. Phantasy Stars Universe has a significantly smaller population, whereas FFXI would be (I assume) bigger.

My friend tried to get me into FFXI back when he was still glued to it. I played for a few hours and couldn't get into it.