Post by Panik8
Spell Power > Critical Rating > Haste Rating > Intellect > mp5 = Spirit.
I'm pretty sure I saw an organized list with the exact answer to your question out there somewhere, I'll try to find it, meanwhile, look at the list of enchants on WoWWiki, it's pretty obvious which ones are better than others for Disc.
Edit: From http://www.tankspot.com/showthread.php?57156-WotLK-Disc-Priest-Guide
(Last edited by Aliena; 10-21-2009 at 03:12 PM., so it might be outdated, although I don't think enchants have changed since then
==Enchants and Gemming==
Discipline priest enchants are very straightforward. I'll list what's generally considered the best choice for each slot.
Head: Arcanum of Burning Mysteries, the 30 Spellpower/20 Critical Strike Rating, available at the Kirin Tor Quartermaster at Revered Reputation would be the best choice. Alternatively you may prefer the Arcanum of Blissful Mending, which adds 30 Spellpower and 10MP5 and is available at the Wyrmrest Accord Quartermaster at Revered Reputation.
Shoulder: Greater Inscription of the Storm, which adds 24 Spellpower and 15 Critical Strike rating and is available at the Sons of Hodir Quartermaster at Exalted Reputation would be the number one choice, or alternatively Greater Inscription of the Crag, same place and rep.
Back: Darkglow (for mana) or Lightweave (for throughput) Embroidery for a tailor, 23 Haste otherwise.
Chest: 10 Stats would be your best choice.
Wrists: 30 Spellpower is the surpreme bracer enchant.
Weapon: 63 Spellpower for a One Hander, 81 for a Staff.
Hands: 28 Spellpower is pretty much the only useful caster enchant to gloves.
Legs: Brilliant Spellthread, which is 50 Spellpower and 20 Spirit is your go-to option.
Feet: Tuskarr's Vitality which adds 15 stamina and a slight run speed increase or alternatively 18 Spirit.
As far as gemming goes, there are different ways to gem your character. You can stack just one stat that you're lacking or that you favor and neglect all others or you can choose to gem for socket bonuses. Gemming pure spellpower is very viable for disc. If you choose to go for socket bonuses though, you should gem Runed Cardinal Rubies in red slots and Luminous Ametrines in yellow slots if you have a chance at the socket bonus for that piece. You'll need at least one blue gem to activate your meta gem, but other than that you may find it best to ignore socket bonuses featuring blue gems and putting Runed Cardinal Rubies instead.
There are several meta gems that you may find interesting. Widely considered as the best choice for healers is the Insightful Earthsiege Diamond, which gives you 21 Intellect and has a chance to restore 600 mana on spellcast. That effect, assuming you cast a spell about every 2 seconds, nets around 75MP5 on average.
Another valid throughput choice would be Ember Skyflare Diamond which gives you 25 spellpower and 2% Intellect and slightly less valuable but still valid - Beaming Earthsiege Diamond, which gives you 21 critical strike rating and 2% Mana.
Edit2: It doesn't take profession enchants into consideration. See what your profession(s) offer as far as enchants go, they're usually better than the "regular" enchants.