When Push Comes to Shove (http://archiveofourown.org/works/116042/chapters/161977) by topaz
- They're Winchesters--they're good at making sure that not dealing with things doesn't slow them down
- this is a threesome (Sam/Dean/OFC) that turns into Wincest with the OFC help bridging them from no-sex to sex. The sex is really hot but the majority of the fic is plot a - the case - and plot b - the brother's relationship.

Ok, I'm going to cry, I was using someone else's bookmarks for all my great Sam/Jess/Dean ones and apparently they took it down. I found these three but I can't remember what the others were called:

As We Walk In Fields of Gold (http://nyxocity.livejournal.com/159130.html) by thenyxie
- this is the sequel. link to the first one is on that page

Postcards (From Easy Street) (http://archiveofourown.org/works/230051) by clex_monkie89
- this - part 2 - has past Sam/Dean, current Sam/Jess, and the direction of Sam/Jess/Dean in part 1. So not sure if it's really what you're looking for, but it's a good (though somewhat OOC) story

Standard Operating Procedure (http://archiveofourown.org/works/131444#main) by keysmash