I have the largest combined collection of audio and text erotic stories available in a plug-in:
http://www.sincontent.com
A small fee of $250 bucks/mo adds our near exclusive plug-in to your site! Also, I thought I would clarify some info in this thread:
1) No idea about
http://eroticlibrary.nu and licenses. I know everything we have is licensed and available nowhere else.
2)
http://ZipContent.com rocks!! They have some stories available for purchase.
3)
http://www.sin-text.com/ - If I'm not mistaken they write custom text... but I'm not sure if they actually have bunches of already written stories for sale.
Cheers!
Brad