(I had to repost this as DISQUS blitzed on me on the blog. Meh, whutever. You can find Night Lords, Alpha Legion, and Dark Angels there already)
Iron Warriors:
All gain the 'Entrenched' special rule. In addition, 1-3 Vindicators/Whirlwinds may be taken per Heavy Support Choice. In Apocalypse, the Iron Warriors will gain a single Orbital Bombardment for free.
Entrenched: The Iron Warriors player gains d6 Barricades at the start of any game, which must be placed after deployment but before the first turn is made. In addition, all units will gain a 5+ Cover Save during the first game turn.
Imperial Fists:
All gain the Stubborn and Stealth special rules. In addition, 1-3 Thunderfire Cannons may be taken per Heavy Support Choice, and 1-3 Dreadnoughts may be taken per Elites choice. In Apocalypse, the Imperial Fists will gain Bunkers for free.
World Eaters:
All gain the Furious Charge, Kill Them All! and Rage special rules though they will ignore Vehicles are not Open Topped for this. In addition, all models must replace their Bolters with a Khornate Chainaxe.
Khornate Chainaxe: This is a CCW which will also remove 1 from any armour save that the opponent takes in close combat against a World Eaters unit - e.g. if a 3 is rolled, it becomes a 2 and so on.
Kill Them All!: The World Eaters will gain +d3 Kill Points or +1 Objective if, by the end of the sixth game turn (at max), they have wiped out 75% of the opponent's army.
Word Bearers:
All models in the army will gain the Demagogue special rule. In addition, Sergeants will automatically gain Locator Beacons for free, and Summoned Lesser Daemons may be taken in the army.
Demagogue: Enemy Units with line of sight to a Word Bearers unit will suffer from -1 Ld (note that this extends to rules such as Mob Rule - +1 Ork is required for Fearless etc). If a Word Bearers HQ or Named Character is within Line of Sight of a friendly unit, that unit will gain +1 Ld.
Thousand Sons:
All models in a Thousand Sons army will count their weapons as -1 AP - for example, Heavy Bolters become AP 3, Bolters AP 4 - and will also gain the Slow and Purposeful special rule. In addition, all Sergeants will have access to the 'Minor Psychic Powers' described below, and all HQ choices will automatically be Psykers which have access to the 'Major Psychic Powers' also described below.
Minor Psychic Powers: A model with access to these powers may select a single power at the beginning of the game before deployment. This does not cost any additional points. A single power may be used per turn unless otherwise noted. Powers: Doombolt, Warptime, Avenger, Force Weapon.
Major Psychic Powers: A model with access to these powers may select up to 3 powers at the beginning of the game before deployment. This costs +30pts for that model unless noted. Up to 2 powers may be used per turn unless otherwise noted. Powers: All SM powers, All CSM powers (except Nurgle's Rot and Lash of Submission).