Sacellum of Nordrassil

Elitist Jerks - Great priest info for both Holy and Disc, Great place for theorycrafting if that's your thing
Plusheal.com - Amazing healing forums for all healing classes really
World of Matticus - Great healing blog. Very Priest oriented
Wow.com - Link to weekly Priest columns of the site, Sometimes geared a little more towards the casual player but some good raid tips every now and again

If anyone has any other sites that they have found helpful please let me know and I would be more than happy to add it to the list