Sweet, all of the speculation about Google unveiling their own chat service appears to be true - I'm signed onto Google Talk right now. It's basically a Jabber server, and you can sign in with your Gmail account info.

If you've got a Gmail account already and a Jabber client (Adium, Fire, Trillian, etc.), here's the connection info you'll need:

Server: talk.google.com
Port: 5222
Username: (like: "foo@gmail.com")
Password:

More details here: smash's world.