One of my friends recently turned me on to Digsby. It's like Trillian, but you can get alerts for MySpace, Facebook and Twitter and chat through Facebook as well. LinkedIn is supposed to be part of it as well, but I can't get that to work for some reason.
Only thing that makes me want to go back to Trillian is Digsby doesn't have IRC capabilities. The developers think IRC will be forthcoming, as well as MySpace IM. I'd love IRC, but I was never the Asylum or OOT channels enough to begin with.
Anyone else tried Digsby yet? I'm liking it so far.