Here's one that'll keep you busy for a while considering it has nearly 500k words. It's completed but it's a crossover with X-men so I hope you don't mind that.
Wolverines, Wendigos and Winchesters by SciFiNutTX https://www.fanfiction.net/s/5155714/1/Wolverines-Wendigos-and-Winchesters (https://www.fanfiction.net/s/5155714/1/Wolverines-Wendigos-and-Winchesters)
summary: SN pre-series / post X-Men Origins: Wolverine - Dean meets Wolverine during a solo hunt, which leads to friendship and a new job. NO SLASH Ch119 - Complete (I mean it this time!)

I'll also give you a link to one of my favorite gen writers: reading https://www.fanfiction.net/u/443241/reading (https://www.fanfiction.net/u/443241/reading)

This is another crossover forgive me. Syndicated SciFi Show, Expanded by claudiapriscus https://www.fanfiction.net/s/5980067/1/Syndicated-SciFi-Show-expanded (https://www.fanfiction.net/s/5980067/1/Syndicated-SciFi-Show-expanded)
summary: Slightly AU for Changing Channels: The Trickster dumps Sam and Dean into Stargate: SG1. They dare to hope they're being allowed a breather episode. After all, it's some sort of fantasy archaeology show, sure to be nice and boring.

I've got more recs on my ffnet account if you want to have a browse. Most should be gen, lots are crossovers too. If there's a pairing, it should be stated somewhere on the summary. Here's the link, enjoy: https://www.fanfiction.net/u/3726155/apokfan (https://www.fanfiction.net/u/3726155/apokfan)