Here are a bunch of fics with erotically intense non-Wincest Sam&Dean stuff. Or at least, I find them to be that way, and I'm probably revealing far, far too many of my weird little kinks in posting this.
The D Word by angstslashhope - This is actually a crossover with The L Word, which I haven't seen, but the point is that Dean gets magically turned into a woman and then has lots of lesbian sex, and that weirds Sam out.
Beach Blanket Poltergeist by hansbekhart - I maybe shouldn't rec this, as I'm not done reading it. Therefore I can neither confirm nor deny whether the end sucks, but the first 2/3 are good, with interesting plot, nice description and characterization, and a sexy wound-binding scene.
Desperately In Need Of A Hobby by apocalypsos - Best summed up in the author's own words: Dean won NaNoWriMo by writing 50,000 words of hardcore lesbian threesome porn, and Sam jerked off to it.
There might also be more if you follow my recs tag. Now, the rest of you jump in with your own additions. Rec stuff you liked. Pimp stuff you wrote yourself. Add to the fun! Use this community!