Here are my favorite long stories, lengths vary, but all are 30k+

Entertaining Angelsl (http://maychorian.livejournal.com/75260.html) Gen A strange boy shows up at Dean and Sam's motel room. Maybe he needs help, or maybe he's there to help them—they can't quite tell. Spoilers through 4.10.

Rain Falling Down (Plus Coming Down on a Sunny Day) (http://maychorian.livejournal.com/136067.html) Gen Castiel goes back in time to stop the Apocalypse. Things go wrong. Things go VERY wrong.

Sound of Something Good (http://archiveofourown.org/works/344513/chapters/559018) Castiel is fighting a war and his seven children are a weakness. So he hires a human bodyguard for them in the hopes that his supernatural enemies won't notice just how inhuman they are. Dean Winchester isn't excited about protecting monsters, but his brother wants him to do something respectable for a while and they're only kids. How ridiculous could it be?

And The Sequel: Ringing Like a Bell (http://archiveofourown.org/works/1103337?view_adult=true) Dean doesn't mind playing house with an angel of God, but sometimes he wonders what Castiel gets out of it. Between the kids, the holidays, and the powers no one is sure he's supposed to have, Dean has plenty of other things to worry about. But none of it seems quite as important as what he's doing with Cas.

I Got Soul by I'm Not a Soldier (http://archiveofourown.org/works/137551/chapters/197455) AU: Castiel is on the road (saving people, helping things) when he meets Dean and realizes that his soul is different - and not just because he's the pastor's son.

http://archiveofourown.org/works/503793/chapters/885401 (http://archiveofourown.org/works/503793/chapters/885401)
In the middle of the barren monster-ridden marches, there is a wall. Encircled by the wall and all its ancient protective symbols there is a small town: a few farms, a few orchards, a few herds of cattle and sheep, a few hundred humans who know that nothing outside the wall is anything but an enemy. The second-worst of the monsters that inhabit their lands are the demons; the very worst are also the most newly arrived, and they are the angels. Dean and Sam Winchester have buried the memories of the silent boy with blue eyes and black wings whom Dean had used to play with as a child, down by the wall, years before any other human ever saw an angel. But when one of the regular travelling pedlars turns out to be hiding wings; when Dean encounters a face he'd stubbornly forgotten for years sneaking into their village at night; when Sam gets hit by a curse that takes his human form away, and Bobby sustains an injury that makes him (by his own rules) less than human, and the behaviour of some humans begins to reveal a darker side, Dean isn’t the only one who will have to struggle to redefine the boundaries between humanity and monstrosity.

Kiss You When It's Dangerous (http://archiveofourown.org/works/561727)When his partner Uriel, betrays him, Federal Agent Castiel Novak is saved from becoming a ritual sacrifice by brothers Dean and Sam Winchester. Discovering the world of the supernatural and learning about werewolves, wendigoes, vampires and things that go bump in the night also leads to learning more about Dean and the strange life he and his brother lead. The more he learns, the more Castiel finds himself drawn into Dean’s world and toward Dean himself.