And now, back to your semi-regularly unscheduled recs . . . .
tiptoe39 is one of the more prolific writers in the SPN fandom. Her fic never ceases to amaze me. For Beyond the Edge and Falling she's teamed up with annundriel, cautionzombies, and obstinatrix. Set in S5, Cas has fallen and faces the fear of not only falling in love with Dean, but hungering for him in ways that merely watching humans have sex has not prepared him for.
There are so few stories from Castiel's POV and fewer that give us such a lyrical and poignant look at Castiel. These authors walk the fine line of schmoop and porn and make it look so easy I'm jealous.