Actus Fidei - "On the very first time that Castiel manifests in front of Father Dean Winchester, he gets as far as "Rejoice, for you are blessed-" before Dean shoots him with a salt-loaded shotgun."

Not only is this just a really good fic in general, I love that, given the ridiculous amount of virgin!Cas fic out there, this fic managed to pull off Castiel seducing virgin priest!Dean. For that it deserves a round of applause.