After Google Talk it time for G mail Chats. Yes, you got it right Google is now coming up with the concept of email chatting. I don't know that how successful would this concept will become in future but the concept is really good specially for the people who cannot use IM's(because they are behind a firewall).
You can get more info on this from this link :
http://mail.google.com/mail/help/chat.html
Google continues to rule, hey microsoft guys r u listening !