The Anvil – Protection 51. No, really. This is a build that the first MT in my first raiding guild used, and with it we cleared several realm first kills all the way up to Naxx 40. This build sacrifices pretty much all damage and Deflection over in Arms, which was a hard sell at the time — when I started main tanking I ended up going with a variant Arms 5/Protection 46 build that gave up Improved Taunt and One-Handed Weapon Spec for those 5 points in Deflection. Either way, this is a spec that says I tank, and I don’t do anything else without either spending gold or bringing a lot of friends with me. But they have a ton of survival in them.
Even though the guide was developed with a hunter, the guide can be followed by any class. Except you have to do your class's quests which aren't a whole lot. I do have full intention to make my guide friendly with all classes in the future by listing all of their steps as well. There will be a toggle that allows you to show which class's steps you want to see in the guide. But this is coming later.