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Ok, here's a video guide how to easily farm reputation with any of the wotlk factions that has a tabard. You need to run in heroic difficulty for this to be effective, it is done in Azjol-Nerub by the second boss.

Remember to put on the correct tabard for the faction you wish to gain reputation with. We did this with a shadowpriest for tagging the mobs, but I'm sure there are other classes capable of doing it as well.
You need one person to tag the mobs and another one to take care of the occational aggro from adds. Other than that you can just fill the party up with friends who wants to gain reputation :)

It works by quickly tagging all the mobs that attacks Hadronox, then when he eats them, you will gain reputation as if you killed them yourself.