GChat

GChat

http://www.windowsphone.com/en-us/store/app/gchat/f9da43e4-9bbb-4a6d-842d-629bd6bdc84b

Gchat supports cool features such as:

- Modern design that integrates with the rest of Windows Phone
- Receive IMs even if the app isn't running with push notifications
- Pin your friends to start and receive tile notifications for each one
- Completely encrypted conversations and support for Google Talk's "off the record" conversations
- New in 1.6: New icon, invisible status, bug fixes, and 24hrs logout timer for Gchat+ users

More info at http://gchatapp.com