I read a really go fic, a really long one, on here a while back. It centered around Cas, who'd fallen pregnant by Dean after Dean's stag party one night. it so happened that Dean was getting married to Lisa (I think it was her) and she didn't know that the whole Dean/Cas thing happened.
Cas goes through with the pregnancy, though when he told Dean, he freaked out and refused, but then slowly come to terms that he loved Cas and everything. Then of course he runs out of the wedding when Cas goes into labor.
There was a sub-plot about Lisa and...I think Jo, finding out they're in love, and they ran off together in the end.
Then of course big mean Daddy Winchester didn't like that Dean was gay and had a baby with Cas and that whole shpeel.
I wish I could find this...it's tearing me apart because what stood out was the fact that each part of the story had really pretty art to go with it!
Someone please find it for me~!