I spend a lot of time in chat (I'm very popular) and sadly all of my friends and colleagues refuse to use the same IM protocol. That's why I eschew iChat and use Adium instead. One of the developers behind Adium gives us a peek at how the beta 1.0 release is shaping up. Before you ask, Adium 1.0 won't support voice/video chat which is just fine with me.
This release looks very promising