It actually wasn't too long ago that I talked about the different race options for priests, but at the time, I didn't talk about the new choices we'd have available to us in Cataclysm. So if you want a new priest with one of the classic choices, feel free to check out this old article. Most of the information is still relevant save for these three changes which you should keep in mind: Perception for humans is gone, Heroic Presence for draenei now only affects the individual player (instead of his or her entire party), and undead will now get mana back when they use Cannibalize.
Since we're here, I might as well throw in my two cents for these little changes. First, the loss of Perception will only hurt priests in PvP. The change to Heroic Presence shouldn't affect healing priests all that much, since we have Glyph of Divine Accuracy for our Smite spam. The switch to Cannibalize is handy for leveling and possibly the most amazing thing for arena.
Now, on to the new racials.
War Stomp Stuns and interrupts have varying levels of usefulness for healers. With an abundance of such abilities existing among tanks and DPS classes, there isn't usually much need for a healing priest to participate in controlling enemies in PvE. PvP is a different story, though, and having War Stomp alongside Holy Word: Chastise is going to make the tauren a reasonable choice for the stun circus that PvP is right now. Tauren priests may also find this additional stun useful in 5-man content when there is more necessity for the healer to be involved with crowd control. (There might also be a higher possibility of bad tank threat in random 5-man dungeons that may require us to stun anything coming our way.)
Endurance Extra health is never a bad thing, though with the increased health pools of Cataclysm, I'm not quite sure how valuable that extra whittling-down time will be to healers in PvP. In PvE, the extra health will make little to no difference.
Nature Resistance Nature resistance is handy but also situational in both PvE and PvP. At the level cap, racial resistance bonuses offer some fantastic damage reduction, but because when you get that damage reduction is variable, I don't think there should be too much weight given to these types of racial traits.
Escape Artist This super-powerful but underappreciated racial ability is handy in both PvE and PvP. In PvE, it serves as a personal Hand of Freedom as long as you're only impaired by a single debuff (which is usually the case in PvE, anyway.) This can be very useful in fights like Ruby Sanctum in which there are movement debuffs built into the encounter mechanics. In PvP, this racial doesn't share a cooldown with a PvP trinket, so it's great for priests; remember that even with higher health pools, we're still going to get focused as healers. The slightly shorter cooldown in comparison to a PvP trinket is great, too.
Expansive Mind There was a lot of debate that this would be the overpowered racial choice for priests in Cataclysm, but with the change from intellect to maximum mana pool, this racial is no longer quite as huge as speculated. The extra mana is slightly noticeable, but what makes it truly powerful is that it shares synergy with our mana-restoring cooldowns like Hymn of Hope and Shadowfiend.
Arcane Resistance Arcane resistance, like nature resistance, isn't the most compelling reason to select a race for your healing priest. It's a perk, and that's about it.
Shortblade Specialization This racial is completely useless for priests, since we don't melee attack too often. If you're trying to stack expertise as a priest, I'm shaking my head at you.
Darkflight Hey, a sprint! I always said priests needed a sprint. Back in the day, I had this deranged theory that priests and warriors were the least-played classes in vanilla WoW because we had no way to increase our movement speed until level 40 when we got our mounts. All the other class had some sort of option to speed up their movement speed or a free mount for compensation, but not priests or warriors! "Rogues don't have it great, but at least they have Sprint!" I said to my friend, who thought I was being silly.
Getting back on track ... A lot has changed since vanilla, but a priest with a sprint is still a nice choice for Cataclysm PvE and PvP. It will assist our mobility and PvP and give us another "oh shit!" button in PvE. Plus, if you're holy, it's a nice followup to Body and Soul if you really need to get away from something.
Viciousness Disc priests are always tagged as the priest who likes crit, and that will hold true in Cataclysm. Holy priests can use crit for proccing Inspiration, but other than that, there is no direct reason to grab it beyond an increased chance at larger heals (you know, critical heals.) This racial is a nice perk if you want to go worgen, but I just don't think it will appeal too much to min-max holy priests.
Aberration Apparently worgen get double the resistance, which will give them quite an edge in PvP. Most races with resistance abilities only have them for one school, so this racial really separates itself from others. PvE priests shouldn't care about this, though.
Rocket Jump This ability is a lot like a forward Disengage (you know that ability hunters use when you tell them you want to take your relationship to the next level? Hmph!). It sends you flying forward to escape all sorts of bad things you can think of. It could also possibly propel you off a cliff, so be careful! (I'm just glad we didn't have this when we were fighting Lich King. Just think of all the accidental deaths there would be during a bodies phase 3 Defile. /shudder.) Overall, this is going to be a very handy ability for priests to suddenly have access to in PvP and PvE. Movement abilities like this are a lot of the reason why engineering was so appealing in Wrath with Nitro Boosts. They give you the option to make up for slower reaction time or to let you get ahead if you do react fast enough.
Rocket Barrage When you're not using Rocket Jump, you can use this damage ability instead (they share a cooldown.) Healers really won't have too much reason to use this, granted, but if you're in out of mana after a long fight, this might be just the thing you need to finish off some boar mob or a warlock.
Time is Money This is the racial every min-max, Alliance raider cried over. A 1 percent buff to haste is appealing to just about everyone, and priests are no exception. Holy and disc priests will both reap benefits from this racial, and it's probably going to be the most desirable racial for players who want to get the most out of their character's racial abilities. If you were planning on going goblin, enjoy!
That about sums it up. If you're really motivated by selecting the best of the best, I'd tie humans and gnomes for Alliance healing priests, and goblin and blood elves for Horde. Everyone has different priorities, though, so what is best for you is what you should stick with.
If you haven't noticed, week after week, I myself play a night elf -- and night elves are probably the worst choice you could make for stats as a priest. I originally had intended to make my character a gnome when Cataclysm came out, but at this point, it doesn't really matter, since I'm not in a raiding guild going for world-first kills and I'm not too competitive with PvP. Add in the armor clipping issues that smaller character models have, and I'm reluctant to swap to anything that isn't a draenei. I just can't stand not having a pretty character. (That doesn't mean I can't have a second gnome priest to melt Fox Van Allen's face with, though.)
Anyway, I have a feeling that a lot of you might have mixed feelings about the whole thing, and you should just go with what works for you. There is no reason to stare at a character you hate for hours on end.
Want more tips for carrying out your priestly duties? Spiritual Guidance has you covered. Check out Cataclysm beta roundup for a walk through on what priests are receiving in Cataclysm; and in preparation for your leveling excursions, check out Levels 80 to 85 as a priest.