It's no secret that Rare is hard at work on the sequel to Banjo-Kazooie, appropriately titled Banjo-Tooie, for the Nintendo 64. Details on the game itself are very sketchy, but it is expected to build off the first game in some way (be it DD or add-on cartridge form).
Rare revealed via its web site that Banjo-Tooie won't make it out until at least the fourth quarter of 1999, saying, "We'll release it when the team's happy with it."
And in a perfect world, that's how every game's release date should be determined.