Mf1438, you've inspired me to write out this erotic fanfiction I've had brewing in my head for a long time. I use Fictionpress.com and Fanfiction.net for all my writing needs. Fictionpress.com is for original fiction, and Fanfiction.net is for fanfiction, obviously. Since they are sister sites, you can have one account for both sites.

They have a rating system so you can write any varying level of raunchy story or fanfic you want, from soft core, all the way to 18+ raunchiness.