They will have flying mounts as part of the Burning Crusade expansion. Now you can go anywhere with your fancy mount, although they will apparently be pretty rare. Check out the Nether Drake. I have to admit that those things look pretty darn cool.
[url=http://www.worldofwarcraft.com/burningcrusade/townhall/netherdrake.html]Flying Mounts: Nether Drakes[/url] (World of Warcraft)