Herald of the Titans

WoD update: For level 80s in WotLK instances, every 1 average item level above 200 gives you 1.67% increased damage/healing and 1% damage mitigation (unless a spell hasn't been squished properly).

Even though this became a Feat of Strength in Cataclysm, it is still obtainable so long as all raid members are level 80 (proof: Aelobin - The Maelstrom (EU)).
Both the achievement and title are account wide since patch 5.0.4

Here's some useful information for those who are attempting this in Cataclysm:

• The key is no longer required to open the door to his room
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• The 1 hour time limit has been removed, so you can fight him for as long as you like
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• Armour items must be ilvl 226 or less, and weapon items (mainhand/offhand/ranged) must be ilvl 232 or less
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• It doesn't matter where your gear is from, so long as it meets the above criteria
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• Epic gems are allowed
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• Reforging is allowed (this includes mastery!)
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• Heirlooms are allowed (although you shouldn't really be using them)
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• The Cata leg enchants, MoP profession enchants and Savage Armor Kits are all allowed
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• You can use Cataclysm consumables (flasks/potions/food/[item=62237]s)
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• It doesn't matter what gear or character level is used to clear the trash and bosses before Algalon

The hardest part about getting this title is finding 10 level 80s with the correct level of gear (or time/motivation to farm the gear). It's a great advantage to have a shadow priest to soak all the Big Bangs with [spell=63229], but a rogue (with Feint, [item=45769], and/or [spell=31230]) works well too.

Healing isn't too hard with 2 tank healers (especially if one is a pally and/or disc priest) and if the collapsing stars are killed at safe times. Average DPS needs to be around 4k each, which is a very easy benchmark to reach with consumables/buffs/reforging.

If you're looking for gear, a good place to start is the JP vendors and craftable items. You can then pick up some easy 219s from the ICC 5mans and ToC5 heroic, along with some 232 weapons from ToC10, Ony10 and the ICC5 mans on heroic.

Update: This has become considerably easier since MoP. Tanks have higher parry from strength and can deal very good damage thanks to the changes to vengeance, and some of the MoP profession bonuses are usable on Herald gear. We even managed to 3 man it, which was soon trumped by Splosion and Dranah who completed it with just 2 Paladins.

Geez To sum this up: • ARMOUR (ALL ARMOR, RINGS, TRINKETS, NECKLACES, CLOAKS) MUST NOT BE HIGHER THAN ILEVEL 226. IT DOES NOT MATTER WHERE YOU GOT IT FROM. • WEAPONS (MAIN HAND, OFF HAND AND RANGED) MUST NOT BE HIGHER THAN ILEVEL 232. IT DOES NOT MATTER WHERE YOU GOT IT FROM. Caps makes it true.

10-man Ulduar: 219 (Few weapons are 226)
10-man Ulduar (Hard): 226
25-man Ulduar: 226 (Weapons 232)
25-man Ulduar (Hard): 239

Basically its all loot from 10-man (Excluding possible Algalon higher item level ones) and non-weapon loot from 25-man normal modes (Again, no Algalon) that you can use for this one.

Edit: I wonder why am I getting downrated for posting correct information...durr.
Editv2: Seems like Yogg drops 226 iLevel stuff on normal mode...