Seems not to be a repost, but it's an old trick...
So, you like the mounts of other races? But you are not extalted with this faction and won't buy tons of rune cloth? Just try the following things.
Quest in the start zone
The quests in the start zone of each factions are very fast done and you can make them mostyl in one round. Especially the quests from lvl 1 - 10 give extraordinary much reputation. I've got about 3000 reputation in one hour.
Extra tipp: Orgrimmar and Darkspear Clan / Gnomeregan and Ironforge have the same start zone, so you get for most of the quests reputation for both factions.
Do the class specific quests again
You can do most of the class specific quests also on the other continent. So I made the voidwalker quest or imp quest on each continent.
For Orgrimmar and Ironforge:
Make some alterac battlegrounds and just concentrate yourself in collecting blood and armor fragments. This is the absolute fastest way to farm reputation for this factions.
Please feel free to send me a pm if you find any mistakes. English is a foreign language for me.