I've used trillian on and off with regular AIM for years. I like trillian because I can log onto multiple AIMs, Yahoos, ICQ, IRC, etc. Also, it has auto-logging, and you can IM from behind away messages (which I know you can do on other clients, but not on regular AIM, which is why I switched back to trillian after using AIM for most of school). Oh, and it has e-mail alerts for yahoo and msn. Very useful.