AlreadyPainfullyGone (http://www.fanfiction.net/u/2549192/AlreadyPainfullyGone) onn ff.net has several... in particular, check out "Me and Mine", "A Series of Unfortunate Texts", "The Devil Wears Prado", "Specimen 001" and "Player 2 Is Ready Now" ... there's several other long ones on her account as well, and most of them are worth a look, but those are the ones I remember particularly and they're the ones I know are completed.

Edited 2012-07-17 12:21 am (UTC)

I second AlreadyPainfullyGone's fics; apart from her most recent one, I think all the others are lengthy and complete, which is always great.

There's also:
The Reluctant Contestant (http://m.fanfiction.net/s/7853540/1) by StArCAtcheR17 (http://m.fanfiction.net/u/2685944/)
AU When Gabriel is hired as a new host for a dating show, Cas has no choice but to follow his brother along as part of the camera crew. Forced at the last minute to be a contestant, he is shocked when Dean Winchester continually refuses to eliminate him.

This one's a WIP, but the author updates pretty regularly (13 chapters in three months!), and it's a really well-characterized and interesting idea, with Cas as a mental patient with Jimmy/Leviathan/Emmanuel/Godstiel/Misha as his other identities. It's really fun to read about their interactions with Dean and the other patients. Dean is a recently-admitted patient with PTSD. The Church Channel (http://www.fanfiction.net/s/8030907/1/The_Church_Channel) by Marie de Sade (http://www.fanfiction.net/u/453074/Marie_de_Sade)
"What's wrong with you?" Sam asked. "What's wrong with me?" Dean hissed back. "You've locked me up in a freaking asylum and my boyfriend has six people living in his head." DID!Cas PTSD!Dean

I've got three ff.net gen casefics bookmarked:

Fix You (http://www.fanfiction.net/s/4678413/1/) - They can fix the impossible, save the innocent, but when it comes to wounds too deep for tears, and scars left on a beating heart, the brothers realize some things may be too broken.
Shiny Happy People (http://www.fanfiction.net/s/6272604/1/Shiny_Happy_People) - An investigation of a newly-formed cult reveals a truckload of weirdness that not even Sam and Dean can take with a straight face. Crack!Fic, Snarky!Adam, spoilers galore.
Agents and Hunters (http://www.fanfiction.net/s/5385224/1/) - Crossover with NCIS. People who work in Abby's lab are never what they seem. And Sam is no exception.

http://blue-fjords.livejournal.com/103072.html

http://swing-set13au.livejournal.com/tag/!welcome

the last link is a rec of destiel au, enjoy :)