Okay, for the sake of ease of reference, here's a sources-cited list of all of the known types of true dragons (true dragons being those with multiple age categories). I also included the neglected planar dragons from Dragon #321 (the adamantine, arboreal, axial, beast, and concordant dragons), and the fire dragon from Dragon #246:
[list reposted on second page]
EDIT: I've decided to go ahead and add the Aquatic, Deshada, and Twilight dragons from Kenzer Co.'s Dangerous Denizens: The Monsters of Tellene book. While not made by WotC, it has the D&D logo, and as with everything that's official D&D that Kenzer makes, WotC looked it over and approved it. So, that seems official enough for me, even if it is second-party.