Gear Selection and Stat Choice:
We're going to start here, as there's been some confusion on how raid tanking Warrior's need to select gear.
Brief overview of primary heroic stats for tanks and what they do:
What is a Mod2 - A Mod2 Stat is any stat underneath the "Heroic Mods" section of your Stat page. These go up based on your Heroic Stats, with a "Softcap" of 400 in it's selected Heroic stat. Once you go over 400 in that heroic stat, you'll begin gaining points in the associated mod2. How many points are needed to increase a mod2 varies depending on the stat, and can be seen by hovering your mouse over the number next to the mod2. A brief description of each:
Accuracy - Used to check against an NPC's Avoidance to determine whether you hit. Governing stat: Dexterity
Avoidance - Used to check against an NPC's Accuracy skill when being attacked. Governing stat: Agility
Combat Effects - Increases chance to proc with all weapons procs, spells, etc. Does not increase chance for sympathetic procs to fire. Governing stat: Dexterity
Damage Shielding - Increases damage done by YOUR damage shields. Governing Stat: Strength
Damage Shield Mitigation - Decreases damage done to you by NPC damage shields. Governing Stat: Heroic Strength
DoT Shielding - Mitigates incoming DoT damage by a fixed percentage. Governing Stat: Intelligence OR Wisdom
Melee Shielding - Mitigates incoming melee damage by a fixed percentage. This is done by reducing an NPC's damage bonus against you. Governing stat: Stamina
Spell Shielding - Mitigates incoming spell damage by a fixed percentage. Governing stat: Intelligence OR Wisdom
Strike Through - Allows a check against a successful NPC defensive ability like Parry or Riposte. If the check succeeds, the skill is bypassed. Governing stat: Agility
Stun Resist - Flat percentage chance to not be stunned. Governing stat: Stamina
The important ones for tanks are AVOIDANCE and SHIELDING.
The Heroic Stats
Heroic Agility - The primary heroic stat for many classes, this affects Dodge %, the Avoidance mod2, Mitigation/Avoidance AC, and Strikethrough.
Heroic Dexterity - Affects Proc rate and Combat Effects (which does the same thing), Riposte % and Parry %. Also affects the "Accuracy" mod2.
Heroic Stamina - Affects maximum hitpoints and the Shielding and Stun Resist mod2s.
Heroic Strength - Affects Attack, block %, and the Damage Shield, Damage shield mitigation mod2s.
Heroic Intelligence/Wisdom - Affects maximum mana pool, mana regen, and the DoT/Spell shielding mod2s.
The important stats for Warriors are Heroic Agility (Hagi) Heroic Dexterity (Hdex) and Heroic Stamina (Hsta), in that order.
So what gear do I pick?
The end goal, as a group geared tank, is to reach 1000+ Heroic Agility at an absolute minimum, 800 Heroic Stamina, and as close to 800 Heroic Dex as possible. With clever gear selection via slot 5/7/8 augs this is attainable. You also want to maximize your AC as much as possible. HP is almost always a secondary consideration to AC!
If you're a Melee DPS, you want to pump Heroic Dexterity and forget everything else. This applies to Rangers, Monks, Rogues, Beastlords, Berserkers, and Bards.
If you're a cloth caster of any kind, you want to pump Heroic Agility. If you are never hit in melee, you may want to consider Heroic Intelligence.
If you're a healer, you should go Agility - or, if you find yourself running out of mana often, Wisdom.