Key Threat Generating Abilities

As a Paladin, the primary Threat generating ability is Righteous Fury and all Holy damage. All of the Paladin's abilities are Holy damage, except the white melee swings. In fact, a Paladin can turn off Righteous Fury after he's done with his adds and just DPS the boss without pulling threat on the boss if the Main Tank has sufficient aggro. Without Righteous Fury, the Prot Paladin is just another DPS in the raid.
Let's first take a look at the key threat generating abilities. These are your biggest assets while generating threat, everything else is fluff when it comes to Threat. That's not to say that other abilities don't have their uses in certain situations but they are your bread and butter.
Avenger's Shield is one of your premiere pulling moves that hits and silences up to 3 targets. It costs quite a bit of mana and if you're getting low, you can skip it. It has a silence and a stun component to it, making it great for pulling caster-types but you'll want to get in there pretty quickly afterward since the stun component won't let them get very far. You must remember to time yourself even if it comes up again you should save it for the next pull since it has the longest cool-down of any of your abilities.
Judgment of Light / Wisdom has 8 seconds cool-down with talents. As a rule of thumb, Holy Paladins will judge Wisdom and Retribution Paladins will judge Light.
Shield of Righteousness will represent 25% of your DPS and is your biggest asset. It can also be used to boost threat on a lone mob that you are trying to taunt off the healers or to solidify your threat in anticipation of a DPS' Area of Effect burst. It should always be used in your rotation and usually right after your Judgment if you are using the Libram of Obstruction. It's the ability that hits the hardest and builds burst aggro. It's the one ability you want to get off on "Skull" before you start building threat on the rest of the mobs. You should also remember that this ability scales directly with Block Value.
Hammer of Righteous is one of your abilities that will benefit the most from a better weapon and more Strength/AP. This is another reason why Paladins are the premiere multi-mob tanking class.
Holy Shield is a very situational ability but on multi-mob pulls, it's essential to keeping aggro while your casters are going all out with Area of Eeffect.
Consecrate is yet another essential ability for multi-mob tanking. Every inch of the ground that Paladins are standing on should be consecrated.
Exorcism is the ability that receives a significant change in patch 3.2 to where it will have a 1.5 second cast time. Cast time makes this very undesirable and getting hit will increase your total cast time by 1sec, 2.5 sec represents almost 2 entire GCDs, and your time could be better spent elsewhere. So, until 3.2 goes live include it whenever it's up but be aware of the upcoming change.
Hammer of Wrath only becomes available once the target is below 20% health and it is a welcome addition to your rotation, again a free, instant cast, single target DPS ability.
Hand of Reckoning is currently only useful as a taunt, it generates initial aggro but if you don't do some actual damage on the target before the taunt wears off you'll lose it and it'll go right back to smacking the healers. After 3.2, this ability will generate real DPS-based threat as well to any target that is not attacking you.