My personal favorites are the one about the married couple who winds up having all kinds of threesomes and foursomes at hot-tub parties and the VERY dirty version of The Little Mermaid. I like to read them out loud to my boyfriend when we're in the tub. It's the BEST.
This site is janky as hell, but it actually has some good stuff, if you don't mind browsing. Click through the "most recents" column. You might find some stories that are awful, but I always manage to find one that's fire.
The Awakening (Kate Chopin)
First published in 1899, this book is one giant volume of blue balls. It follows Edna, a bored housewife who is unsatisfied with her marriage. She finds herself overtaken by this hot, young dude and goes for it. There is so much innuendo and the sex is only ever alluded to. It is HOT.
In case you missed this mandatory reading in high school, spoiler alert: it gets pretty dark in the end, so if you're trying to keep it strictly sexual, skip the last scene.