Adium. It has allowed me to cut down on my AIM time quite a bit. I really only talk to 3-4 people consistently, the rest, I don't talk to much at all.
I love being able to talk with an away up, saves me so much trouble and conversations I don't want to have. The idle time thing is wonderful too. I'll never go back to iChat, till the girlfriend gets a Mac at least, than we'll do the AV thing
(Not what you think :P)