D/C fics with Sam are my favs :D
Here are some:

- If you ever get close to a human and human behavior (be ready to get confused) (http://bree-black.livejournal.com/24040.html): In the weeks following the almost-Apocalypse, the men who fought to save humanity realize they have no idea how to be human themselves. While Dean Winchester struggles to make a place for himself in small town Indiana, his brother and his former guardian angel watch from a safe distance. Sam finds himself literally and painfully caught between his old life and Hell, while Castiel – fully human for the first time – copes with freedom, frailty and an intense new set of emotions. Reluctant to reveal their weaknesses to Dean, they hover around the edges of his new life. That is, until they sense that something darker and more sinister is watching Dean as well.

- Face to Face with the Skies (http://quidquoprose.livejournal.com/22157.html): (Set right after 4.22) Castiel was not killed by Raphael on the night of Lucifer’s release. Instead, he’s sent to the year 1996 and encounters the Winchesters. Unable to return to the present, Castiel resigns himself to traveling with them on their hunts across the states.
Meanwhile in the year 2008, Dean has barely gotten used to being back in the land of the living when he gets the biggest shock of his life; the man he fell in love with when he was eighteen has seemingly come back from the grave as well, claiming to be an angel of the Lord. The thing is, he doesn’t have a clue who Dean is.

- Our bodies, possessed by light (http://obstinatrix.livejournal.com/110413.html): Purged of all his souls, Castiel is a changed being, stronger than an angel and too powerful for Jimmy's body to contain. Happily, there's an archangel's vessel on hand, and he could use fixing, too. Dean isn't too happy about the idea of his brother acting as a vessel for Castiel, and Sam can guess why, but it isn't until Castiel gets inside his head and they learn to share the vessel -- and their thoughts -- that Sam realises Cas is as in love with Dean as Dean is with him. It's unfortunate that there's nothing much to be done about it now, but Castiel will get another vessel soon. The Winchesters will make damn sure of that. In the meantime, it's up to the three of them to establish their own strange accord, and Dean realises more fully than ever that it's Castiel, and not his vessel, that he loves.

The Girlfriend Experience by rageprufrock
http://archiveofourown.org/works/91894?view_adult=true
While it's not like Dean hasn't had a couple of truly regrettable hit-and-runs in his sexual history, this is probably the saddest fucking thing that has ever happened to him.

Also the stories of the gentle fall verse
http://www.delicious.com/dirtydancer14/dean/castiel+verse%2521storiesofthegentlefall


And by the same author Right Up Over the Wire by liadan14
http://liadan14.livejournal.com/42274.html
When Sam finds out about them he's convinced that Dean's possessed/bespelled/being controlled by some supernatural force, and Dean has to come to terms with the fact that yeah, he is actually kinda into guys, before he's able to make Sam believe he's still himself.

I love this a lot, a Dean/Cas with plenty of Sam.

The distance of the setting sun (http://murron.livejournal.com/165038.html) by murron.