Discipline priest PvP Discipline has been the PvP healing spec for a long time, with a playstyle that is geared towards mitigation, high mobility, high survivability, and support. Many of the talents in the tree are focused at producing more efficient shields and special effects playing off them. While there aren't a lot of offensive options, you'll see the developers' intent to make using offensive spells part of your repertoire, so they become rewarding rather than penalizing.

• Improved Power Word: Shield - If you're a discipline priest, you'll be casting Power Word: Shield. A lot. It's discipline's signature spell, allowing you to be extremely mobile in PvP. Casting instant heals such as Renew and Prayer of Mending in between shields make discipline quite arguably the most mobile healing spec, or maybe on par with restoration druids.
• Twin Disciplines - I'm putting this talent on this list even if it's just a damage increase mostly because at such an accessible tier, it's an attractive option to shadow priests for their sub-spec. Discipline priests will pick it up for the healing bonus and, hey, a small boost to -- bam! -- Smite. Ok, not really, but it's a good talent that's slightly different from its original iteration which made only instant-cast spells better.
• Evangelism and Archangel - Here's where things begin to get a little more funky. While the talent is attractive to shadow priests for obvious reasons, the spell gives incentives to casting Smite during dead times. More Smite means cheaper and more damaging Smites, Holy Fires, and Penances. It's not going to get you into groups as DPS, but it's certainly going to make casting those offensive spells worth it when your team's doing pretty well without heals. Archangel gives back a little mana and better passive healing, and you'll want to keep activating it every time you have full stacks of Evangelism.
• Inner Sanctum - This is a talent that you should pick up mostly because it will become better in Cataclysm. The spell damage reduction is cool for now, but it will shine even more in the long fights of Cataclysm PvP. Furthermore, it also grants a 6 percent bonus to Inner Will, an ability you'll pick up at level 83 which reduces the cost of instant cast spells and increases your movement speed. With Inner Sanctum, your speed increase is bumped up to 16 percent, which is actually slightly higher than that standard 15 percent passive speed increase that most classes get. This is your PvP buff, and you will learn to love it.
• Soul Warding - Faster is better, as I always say, and this is why most cooldown reductions qualify as PvP talents in my book. This talent no longer eliminates Power Word: Shield's cooldown, but that was reduced to 3 seconds down from 4, which makes a 2 second reduction from Soul Warding almost as good as the previous version on paper. In reality, though, it will take some time for your cast to travel to the server before it starts the cooldown. That pushes your effective cooldown from 1 second to anywhere from 1.2 to 1.6 seconds depending on your latency. That means even if your haste lowers your GCD below that number, you still won't be able to cast another Power Word: Shield. Overall, the talent has been nerfed (it no longer reduces mana cost, either), but you still need it so spend those two points here.
• Power Infusion - Activated long-cooldown spells add spice to PvP encounters, and most of the time you'll need that extra punch. Power Infusion is a haste and discount spell, which is great for those clutch situations where you actually need to stop and throw out some big, long cast heals. The cool part about Power Infusion, though, is that you can actually cast it on a teammate, such as that hard-hitting mage for some tag team enemy obliteration.
• Atonement - So. Much. Fun. What this talent basically does is turn your Smites into heals, allowing you to keep on Smiting opponents and healing your team at the same time. The harder you hit with Smite (this is where Twin Disciplines and Evangelism start to pay off) the better your heal will be. In the battlegrounds, you can contribute to the fight by Smiting your allies' targets and healing them in the process. That's almost freakishly unfair. You may want to glyph with Glyph of Divine Accuracy (major), which boosts your hit with Smite by a whopping 18 percent. Since you won't have much hit in all that healing gear, this glyph turns your Smites into more accurate heals. If you want to hit harder and heal bigger, you might want to use Glyph of Smite (major), too. This should transform your playstyle into a more aggressive support healer role that looks to use offensive spells as a means to heal.
• Inner Focus - The good news is that the cooldown of this activated ability has been reduced to 45 seconds from the original 3 minutes. The bad news is that it no longer affects any spell but select heals. That said, it's a one point investment to cast a free spell with a higher crit chance every 45 seconds. We like free and we like higher crit.
• Rapture - This is a talent you're supposed to get mostly because, well, you cast shields and shield disappear at some point. Because it also procs mana gain when the shield is dispelled, it becomes even more valuable in PvP as mana management is important in the longevity fights of Cataclysm.
• Reflective Shield - At some point, of course, your opponents will bear down on you and you'll probably get knocked around a few times on the battlefield. That's cool because you'll pick up Reflective Shield, which means anyone who does try to damage you will be hurting themselves even before they break through. This won't work for shields cast on others, but it's great passive damage for just two points.
• Pain Suppression - This talent single-handedly catapulted discipline priests into the PvP elite and remains the best PvP talent in the tree. The effect is simple: it will keep you or your friends alive. Pair it with Glyph of Pain Suppression (major) which allows you to cast Pain Suppression while stunned and you've got a truly topnotch PvP ability.
• Train of Thought - This is a great talent that works for both the defensive- and offensive-minded caster. We'll skip the first effect because it's a tiny bonus for when you actually want to cast Greater Heal. On the other hand, the second effect invites you to keep casting Smite to get to another Penance quicker -- you'll have Glyph of Penance (prime) on, too, of course. Now keep in mind that Penance can also be used offensively, making it possible to chain cast Smite to get to Penance, with all the bonuses that come with casting Smite.
• Focused Will - "Hard to kill" would probably be a decent way to describe discipline priests. Focused Will adds "freaking" to that descriptor. The tricky thing about this talent is that it only procs with an attack that actually damages you for 10 percent of your health or more. This means that if you absorb damage through a shield and only get hurt for about 9 percent of your health after mitigation, this talent won't trigger. It's still a useful talent for when your shields fall off before Weakened Soul has expired.