All the healing classes, including Discipline Priests, are fine right now.
Druids just got hit with a nerf, but even they are still ok.
Power Word: Shield "Weakened Soul" debuff duration has been increased, and it costs a lot of mana now.
No more bubble botting.
You still get mana back from Rapture, but it has a cooldown, so you can't get more than a set amount every so often.
Here is a tracker for that:
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http://www.curse.com/addons/wow/ingelasrapture
Mastery is a new stat that strengthens your core ability. For Discipline that means shields.
You stack shields with critical heals using Divine Aegis.
Prayer of Healing is a guaranteed crit so spam it on a group when you want to build a shield.
Power Word: Barrier is the new raid cooldown Discipline has.
It's like a Pain Suppression AOE (but you can use it on a single person if you want to).
It stacks with Pain Suppression too, if necessary.
Flash Heal is no longer favored unless you have mana to burn.
Use Heal or Greater Heal if you can.
Alternately, there is a new talent called "atonement" that will "smart heal" the lowest health friendly player near your smite/holy fire target.
The heal is in proportion to the amount of damage dealt, up to 100% depending on talents.
If you go atonement spec, then pick up the glyph of Divine Accuracy, which will increase your hit rating for Smite.
There is another talent called Evangelism that gives you a little bit of mana back and increases your healing throughput by 15% or so if you do it right.
You can gain stacks of evangelism by smiting or using Holy Fire.
Divine Hymn is kind of a weak heal for Discipline, but combined with a potion (Volcanic Potion) it works well.
Also, see
http://askmrrobot.com for reforging, gemming, and gearing tips.
