A good chain to do is Archivist Gardford ( hu Strat) -> then go back to Hu strat and loto head off of final boss -> then get quest to kill Baron in UD strat. That nets a good staff. As well as multiple chances at like Righteous orbs, Devout gloves/legs, and other such things.
While doing that you'll prolly want to do plagued flesh, and "Of love and Family" or whatever its called. The later starts up on the NE end of the river seperating WPL and EPL, and its pre-reqs invovle a lot of killing of mobs in EPL, but its worth it since even at 60 you get like 25-30g for turning in all the steps with the xp to gold thing. Reward ofr that is a ring with some minor stats and +37 healing.
Dire Maul has some quests mostly with shitty rewards for a priest but the drops are top notch. midntap talisman Padre's pants among others from west. Orge magi stuff, channelign rod form north etc. Along the way you can do the quests. Of particular importance is to get the quest that will enable you to turn in DM librams in the future... I don't know where it starts for Horde side though.
In short check out
http://69.41.171.43/priest.htm
It has a good listing of all the drops you might want froma given instance, and some of the major quest rewards that might entice you to go. bear in mind most of those quests have pre-requisties so be sure to check them out too.