www.trillian.cc
You can use AIM, ICQ, Yahoo Messenger, MSN Instant messenger, and IRC Chat all at once, I talk to Graal buddies who all have AIM, ICQ, and stuff like that all spread out, it works wonders, and it is it's own program too, so if you hate ICQ you can now use it to talk to buds who use ICQ without having to mess with the ICQ program (or its popups)