Color me...blue. I've always been a sucker for blue dragons. Not sure if it's simply the color, or the way they are typically depicted in the various editions of the MM, but there is just something about them that makes me nod my head and grin. The dry, arid desert air, the cool underground lair, the crackling of lightning breath unleashed by an angry blue. I imagine a clever blue could whip up a mini-sandstorm with his wings, making the fight even more difficult for the players.
Reds are the iconic pic, of course. And I've always been partial to black and green dragons as well - how many adventurers are prepped to defend against acid or gas when a dragon makes an unexpected appearance? That's what I thought. Oh, and more than once we have had to deal with Dragon Turtles while transiting one body of water or another. Nasty business, those can be.
And lastly, in a totally shameless bit of self-promotion, you can still find my Instant Dragon Generator on WoTC's website. Nothing fancy or too involved, really - the bulk of the work was coming up with all the different lair descriptions. If you are looking for something meatier, check out this link to the Unexpurgated Dragon Generator I saw on Swords & Dorkery.