When you first hit Heroics, you won't generally be completely AOE tanking. You will probably need at least one CC because the mobs can hit damn hard. With that said, with the changes to the warrior class, there is not excuse not to be able to AOE tank. Thunderclap is pretty awesome now and for me crits for over 1000.
Thunderclap is probably your most important ability for AOE tanking. Not only does it do some decent damage, but it also reduces the attack speed of things hitting you. Getting hit less=good (at least in content you dont outgear by a ton).
Shockwave is the new hotness for Prot Warriors. I does a bunch of damage and also stuns the targets for a short amount of time. My Shockwaves crit for well over 3k damage. The cooldown on this ability is not incredibly short, so you will have to choose when to use it.
Demoralizing Shout is still as important as ever when AOE tanking. Making things hit you less hard is good. If you get smashed, so will the rest of the group.
Cleave is one of the old standbys for AOE tanking and is still a good option.
Glyph of Sunder will also help a lot when AOE tanking. It will place a sunder on a nearby bad guy when you sunder your main target. Its like the old tab target AOE tanking only dumbed down.
Generally what I like to do it charge in, thunder clap, backup, and then Shockwave. While they are stunned you can throw up a demo shout. Follow that with another thunderclap, and do you regular threat rotation on the main target. You can always tabe sunder if you like or throw in a cleave or two. If the AOE pack is getting read to go down, dont blow your Shockwave cooldown again. Make sure to wait until the next group for that nice big chunk of AOE threat.
AOE tanking is just that...AOE tanking. You are using your AOE and the DPS is probably doing the same. If you want them to focus fire a target, make sure to state that or mark it. If you dont, and they pull aggro, it is your fault Mr. Tanky.
As always, tank responsibly. This message has been paid for by Darraxus for President.