Probably you know it already: A free service for Google called Google talk that permits you to talk with and send instant messages to your friends. This service is in beta and requires a Gmail username and password. So to use it, you have to have a Gmail account.

There is a good feature and a missing feature with Google talk:
The missing one: Google Talk is not multi language. It is currently available in English only.
The Good one is: No ads, no pop-ups or clutter, just a clean and simple interface.

A good news for GAIM users: they can use GAIM to connect to the Google Talk service

For more information about Google Talk:

Getting Started: http://www.google.com/talk/start.html

Download: http://www.google.com/talk/