meus_venator's Prime comes to mind, as both Sam and Dean are at separate times enslaved, and fighting against it.

Though not explicitly labeled "slave fic," my own series, beginning with More Than Words, deals with government sanctioned indenture. It's also linked here on LJ in the side panel of my journal. There's a timestamp, and two sequels that deal with abolishing the practice.

Edited 2016-04-25 12:02 am (UTC)

thank you so much <3

Delicious isn't working for me at the moment, and so far I've only transferred about half my links to pinboard, but here's a couple. I can probably send more once delicious is back up and running.

Flightless Bird (http://foolsdance.livejournal.com/9291.html) by foolsdance: "Jensen receives an unwelcome inheritance in the form of a pretty young body slave named Jared. Unable to free him and unwilling to use the person in his care despite his attraction to him, Jensen is stuck between a rock and a hard place. Jared, meanwhile, doesn't know what to make of his confusing new owner, who has yet to punish him despite his many mistakes and doesn't seem to want him in his bed." (slave!Jared)

Things We Can't Untie (http://magellanflies.livejournal.com/18225.html) by magellanflies: "Jensen Ackles thinks he's prepared for his new job, training political prisoners as sex slaves for the wealthy elite. But when he meets his first client, a gorgeous, intriguing kid named Jared, his own doubts about his profession begin to catch up with him. Soon, he's developing a disconcerting attachment to Jared, and struggling with the full implications of his career." (slave!Jared)

Two more, if you don't mind Sam/Dean:

Kant's Dove (http://tryfanstone.co.uk/kantsdove.htm) by jaytryfanstone: "In a dystopian paradise angel Inquisitor Samuel and rogue human Dean are uneasy allies. Together, they could knock their world from its foundations, but both of them have secrets to keep." It's been awhile since I read this one, but I don't think humans are slaves exactly, but they're definitely an oppressed class, and Dean's a freedom fighter. (raised!apart Sam/Dean AU)

I Think Therefore I Am (http://archiveofourown.org/works/464518) by ochsun: "Dean is a privileged member of the dwindling original population of North America that has been decimated by viral outbreaks and low birth rates. Human clones have been created to bolster the work force. They are a segregated underclass relegated to the status of soulless drones by their Geneticore creators and by powerful religious groups like the Mothers Union, who consider themselves to be the blessed vessels of God’s greatest creation: the human soul. This is a story about the complicated relationship between two boys who are forced to grow up into hardened soldiers by a society teetering on the brink of civil war." (sort of a slave!fic? Lots of freedom fighting, etc)

Thank you! I enjoy your reccs immensely from other posts and appreciate the links. I've read (recently) the j2 fics, but not the S/D as they are usually not my cuppa, but the last link seemed particularly interesting.

If more fine to mind please do feel free to share :)

Deathknell verse - it's unfinished but that doesn't matter, one of my absolute favourite stories
http://beanside.livejournal.com/215475.html

I love that verse. Reaching the last post and seeing it unfinished still counts as one of this fandom's tragedies :(.
I probably will return to it just out of masochistic nostalgia. Thank you!