Here are just a few of my favorite Sam/Dean fics. A lot of these have probably been rec'd already, but I love the feel of these stories. They all have a tense atmosphere and are written beautifully.
You're a Beautiful, Beautiful Fucked Up Man by
entangled_nowRating: NC-17
Summary: Dean's mouth smells like cheap lipstick and something that might be plums
How It Is by
gwennie3579Rating: NC-17
Summary: This is how it starts...
Maybe It's Just Us by
gatorgrrrlRating: R
Warning: underage!Sam
Summary: Sam’s too big for the mold he’s been forced into and too bright for the dark world they live in. But Dean doesn’t know how to let him go.
Witching Hour by
ash_carpenterRating: NC-17
Summary: Sam gets an insistent wake-up call from Dean...
Ruins of Roosevelt by
leestoneRating: NC-17
Summary: Same city, different devil. And Sam just keeps saying Yes.
If All Roads Were Blind by
nilynRating: NC-17
Summary: They both know what he's about to say, and Dean's been fighting with himself on the issue well before Sam's latest near-death experience. On one hand, Sam is an adult, his hunting partner, and Dean shouldn't be babying him. On the other, Sam is Dean's world, the only family he has left, and he'll be damned if he lets Sam beat him in the live-fast-die-young Olympics that is this life.
You're in a car with a beautiful boy by
wnchsterRating: R
Summary: They call you Sam and you fall in love with your brother. He calls you Sammy and it's more about restraining yourself than it is about that certain feeling in your soul.
A Million Miles From Home: Goodbye by
thatsleon_etcRating: NC-17
Summary: This is the night Dean doesn't say goodbye.
A Skeleton Inside My Skin by
oddishlyRating: NC-17
Warning: underage!Sam
Summary: Sam is just confused. It's not an excuse Dean gets to use on himself.
Choir of Furies by
atanih88Rating: NC-17
Word Count: 32K+
Summary: The nightmares Dean has been having aren't his. They belong to Sam. As the dreams begin to escalate, it starts affecting the brothers' awareness of each other, leaving both Sam and Dean struggling to find a new balance in their relationship as the last of their boundaries are stripped from it.