vent and xfire work good
vent requires a dedicated server for team chat

I'm kind of fond of Steam's chat client.

Sorry, I meant voice chat. Thanks for the suggestions. I'll give xfire a shot.

Thanks!

Skype is horrible for use to talk with friends for a video game. Look at the system resources you are using and its a constant feed. Annoying. Team Speak is alright, Ventrilo is by far the better choice. You can host your self for some friends for free so long as there are less then 8 people on the server. If you want to allow more you have to go and rent a server which doesn't cost much per month. and then you get issued an IP and port to give to who ever you want to join your server and you get to name it and establish your rules and such and codecs for the server so on and so on.

I use steam and it works fine.