So maybe this could work, but I have not tested it to see how much it would make.
Anyway, here is the idea. The dungeon in Borean Tundra, known as The Oculus, holds many dragons within it that give rep to the player (Each one on a normal run gives 1 or 5 rep per kill), anyway, buy a tabard from the faction that you would like to earn rep for, and wear it as you are inside the instance killing these dragons. All the rep will be given to that faction.
This is a great instance for this because it is insanely easy for a level 80 instance, and you do not need to set the dungeon to Heroic. My group was clearing this dungeon in about 40 minutes max.
Rinse and repeat, and this dungeon has the possibility to earn tons of rep for your faction.