LiveJournal has recently started running a jabber server! [ technical info | slightly less technical info ] This basically means that you can IM your LJ friends through LiveJournal's server: your buddy list is automatically populated with all of your LJ mutual friends.
This works through a service called Jabber, which is a free and distributed protocol that's also used by Google Talk (and which is in contrast to AIM, a proprietary and centralized protocol). You can use Jabber via Gaim, Trillian (Pro only), iChat, Adium, and several other programs. If you don't have any of these, I recommend Psi as a standalone Jabber client, or one of the above (I've never used any of them much) for something that integrates Jabber with AIM.
It's all Alpha, so the server drops sometimes, and some key features (removing people from your buddy list so they don't see you as online) don't exist yet. But it's still really neat! Go check it out!
And I'm running a Jabber client for the first time. So if you use Jabber regularly through some other server, let me know what your ID is so I can add you. (Or try to figure out how, at least.)