Homepage of Adium
Shame on me for not having done a blog entry for Adium yet.
What's Adium? It's the most known duck in the Mac world...no seriously, it is like Trillian or Pidgin for the Mac. It is a multi-protocol instant messenger that is highly customizable and certainly the best instant messenger, in my opinion. It should be one of the first apps that gets installed on a new switcher's Mac.
Only downside of Adium is the fact that it does not support AV chat - yet.
According to the developers' blog they are currently working on implementing this feature. I'd say with AV chat there won't be any competition for Adium.