From: Viper114 | #003
Normal instances, generally no with some exceptions. Pre-cata I can't think of anything that would drop in normal mode, but Wrath Heroics had a few that had rare chance to drop mounts and one that guaranteed to drop a mount (Bronze Drake, Heroic Culling of Stratholme). Cataclysm offers two mounts that can drop in the normal versions of instances (Drake of the North Wind from Altairus in VP, Vitreous Stone Drake from Slabhide in SC) but they're extremely rare (less than 1% chance I believe).
Outside instances there are several mounts to find. Some are dropped from extremely rare spawns (Phosphorescent Stone Drake from Aeonaxx, Time Lost Proto Drake from Time Lost Proto Drake), some are available after doing several days worth of dailies and then buying them when you hit Exalted rep. There are so many of them currently available, I would suggest checking out http://warcraftmounts.com/ to browse around.
Thanks! :D
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