As of a little while ago, the new Zelda game set to be released in late 2005 was given it's official name. The new game will be called The Legend of Zelda: Twilight Princess, and as far as I know of, it should be released sometime in November this year, and I know for a fact that it will be for the complex system that has been out since 2002: the Nintendo GameCube. The game will mark the return of our OoT hero, Adult Link, and the graphics will be a major revamp of the OoT graphics. They will be more 3-dimensional and, as far as I know of, shouldn't have the flat-looking tree figures, like OoT and MM had.
I don't know what the story is yet, but I know for a fact that players will use Adult Link throughout the game. This is an opportunity that we haven't seen since we pulled up the Master Sword in the hit 1998 game, and we get to do it throughout the whole game now.
Let's hope that LOZ: TP is the best game so far, which should be true, seeing that the screenshots show the most action you could get from a Zelda game. November is 5 months away now. As I find out more information, I will post it.