I guess our view on what is "in character" for Sam and Dean in fics strongly depends on the way we see them, so what is "in character" for one reader might not be for another. Anyway, aside from some of the fics others already recced, the following felt really in character for me:
Driving Down the Darkness (http://nutkin.livejournal.com/35088.html) by nutkin
Exact Change (http://documents.mx/documents/exact-change-by-yourperiphery.html) by yourperiphery
Midwinter Montana (http://www.sinful-desire.org/archive/viewstory.php?sid=2433&warning=5) by Morgan
The Things We Carry With Us (http://archiveofourown.org/works/267862) by lovesrain44
Strong Black Vine (http://archiveofourown.org/works/4413944) by shaenie
no subject
Driving Down the Darkness (http://nutkin.livejournal.com/35088.html) by
Exact Change (http://documents.mx/documents/exact-change-by-yourperiphery.html) by yourperiphery
Midwinter Montana (http://www.sinful-desire.org/archive/viewstory.php?sid=2433&warning=5) by Morgan
The Things We Carry With Us (http://archiveofourown.org/works/267862) by
Strong Black Vine (http://archiveofourown.org/works/4413944) by shaenie