The Argent Dawn

To get the repeatable Argent Dawn quests:
To be able to do the quests Aberrations of Bone and Annals of the Silver Hand you must first complete the following quests that are initiated by Fiona who is standing at the bridge that connects the Eastern Plaguelands and Western Plaguelands.

Tarenar Sunstrike -> What I Do Best -> A Gift For Fiona
Gidwin Goldbraids -> Just Encased -> Greasing the Wheel

Once these two chains are completed, you can do Onward, to Light's Hope Chapel which will take you to 'Crown Guard Tower'. Once there you must complete Traveling Companions (he's at the top of the tower) and then complete his quest (Rough Roads) before being able to continue on to the next tower via the quest The Trek Continues. Once there, you can pick up the quest Boys Will Be Boys from Fiona. Go to 'Light's Hope Chapel' and complete the following quest line:

A Boyhood Dream -> Argent Call: The Trial of the Crypt

After completing the latter of these two quests, you will be set to revered (+0 reputation if you're already over 0/21000 revered) and Lord Raymond George will appear at the back of the chapel and will provide you with the two repeatable quests that give 2,000 Argent Dawn reputation per hand-in.

Best Grinding Method:
I have just got to exalted on my protection paladin and found something interesting (I was level 85 and used a flying mount to get around):

When doing both quests it took me just over 12 minutes to do, starting from standing in front of Lord Raymond George (the quest giver) and ending in front of him. However, if I only did Aberrations of Bone, it took me around 5 minutes 30 seconds to complete meaning it's actually quicker to spam Rattlegore kills than to try doing both.

The best way to complete Aberrations of Bone is once you've got to Scholomance, jump down from the 'bridge' and stay as close to the wall as you can (there's a little ledge in the pit below which you'll land on and it will greatly reduce the chance of pulling anything). Then run up the steps and over to the room with whelplings in; once in this room, jump down the hole on your left and then run over and kill Rattlegore. After that there's only really one way back to the entrance. It shaves off about 30 seconds or so taking this route to Rattlegore.

The fastest way to exalted now (post Shattering) is to pick up the quest Annals of the Silver Hand from Lord Raymond George (if you're a shaman, set your hearth at the Inn so you can Astral Recall back!).

Make your way through Stratholme and clear down towards The Crimson Throne and collect the book and make your way back to hand in.

Pick up the quest again and head back, you don't need to reset the instance to collect a new book. Will take 11 runs from revered to exalted.

You get 150 rep for a corruptor's scourgestone+valor token. Doing a baron run nets you 5 guaranteed, plus another from the magistrate who's right there, so you may as well kill him. That's 6x150=900 rep right there. If you can do it in under 45 minutes, there's another 300 rep. By the time you hit 80, and given the changes they're planning for itemization, talents, etc... There isn't much reason anyone shouldn't be able to solo Baron runs, if not 45-min runs. Sure, it might take a few of them, but people who want exalted with a faction have done crazier things in the past.