On my holy priest (2nd priest), I went tailoring and enchanting. Tailoring got me a nice three piece set of epics without ever setting foot into an instance, it just requires about eight billion bolts of cloth. (Dis)enchanting was more of a money maker than anything else. The +20 healing to rings and +12 spell damage to rings are nice, however I wouldn't have leveled enchanting from 1-375 just for those enchants. Everything else you can get from other enchanters.
On my shadow priest (3rd priest), I went tailoring and alchemy. The Frozen Shadowweave Boots are the best you can get at the moment. The robe and shoulders aren't too shabby either. I chose alchemy for the alchemist stone also. The stats are nice, however what really caught my attention is the +40% on health/mana pots. As a shadow priest, I'm not going to spend much time outside of the five-second rule. Well, maybe during bio breaks and running to the summoning stone. If you're not casting during fights, you're not helping your raid much. Unlike warlocks, we don't have life tap/drain life combo or even drain mana. So the only way you're getting more mana to regen mana for your raid is potting. Why is that +40% so important? Think downing a pot on every cooldown for a 4 hour raid.
Hope that helps a little.