The advice given makes a lot of sense, but I wanted something that was fun and had some side benefits, so I took Enchanting and Engineering. Enchanting pays all my bills, and I've never directly enchanted anything for another player, or spammed the trade channel LFW. I've sold some enchants in the AH, since the option to cast enchants on vellum was added.
For cash flow, I use the Auctioneer Mod to scan the Auction House for stuff to disenchant, and then sell stacks of enchanting materials back to the AH. This pretty much allows me to buy whatever I need for all of my alts. I just buy the materials for my secondary proffessions, upgrade gear whenever I want to, and cast all of my own enchants on my gear.
My Priest is lvl 67 now, and I'm going to build the Gnomish Flying Machine flying mount when I hit 70. The Noise machine trinket is pretty good, I don't really need a second shield, but a lot of times it procs before I get to PW:S in my rotation, and it will proc in an ambush situation. I'm using the Powerheal 4000 epic helm right now, and I dropped a +25SP gem in the meta socket. Another plus is some of the explosixes give shadow spec a minor AOE with the saronite bombs, explosive decoy, etc.
Edited, Apr 15th 2009 8:40am by Kuthela