Unfortunately there's still no news about the exact date of the Third Season's debut, but we do have a nice little tidbit. Apparently, a new Avatar game is in the works, this time based on the events of the second season, Book of Earth. In this second videogame, Aang the Avatar and his friends must team up to defend the Greatest City in the Earth Kingdom from a deadly Fire Nation threat. Entitled Avatar: The Burning Earth, this will hopefully improve upon the previous game. All I can say is... Toph had better be present and playable. Heheh.
Anyways, for some nice Avatar tidbits, I highly recommend heading on over to Avatarspirit.net to check out stuff like a three-part interview with Avatar creators Bryan Konietzko and Michael Dante DiMartino that reveals quite a bit of stuff about the series, characters and behind-the-scenes stuff (but of course, nothing about the Third Season's release date).
And so... back to waiting. Darn it.