It really depends on what you're willing to do to get one. There's a number of options that don't take a lot of time per day (although it may take a little while to get them total). For example:
There are several you can get from doing dailies:
Flameward Hippogryph (Molten Front dailies)
Nether Drakes (Netherwing dailies, several different colors)
Green Proto-Drake (Sholazar Basin dailies until you can buy the egg, which has a chance for the mount to drop every three days)
Cloud Serpents (Order of the Cloud Serpent dailies, several colors)
Drake of the West Wind (Tol Barad dailies)
From reputation:
Cenarion War Hippogryph (Cenarion Expedition exalted)
Red Drake (Wyrmrest Accord exalted)
From dungeons/raids that are easily soloed, although they're only a small drop chance:
Blue Proto-Drake (heroic Utgarde Pinnacle)
Bronze Drake (heroic Culling of Stratholme, always drops if you beat the time limit)
Fiery Warhorse (Karazhan--and yes, it flies)
Vitreous Stone Drake (Stonecore, either mode)
From raids you may need a group for, but only take a few minutes with one:
Onyxian Drake (Onyxia, either mode)
Blue Drake (Malygos, 10-man)
Azure Drake (Malygos, either mode)
Black Drake (Sartharion, 10-man with three drakes alive, always drops)
Twilight Drake (Sartharion, 25-man with three drakes alive, always drops)
This list isn't all-inclusive, but this is what I thought of.