For the adult webmasters out there that also have mainstream sites, check out
http://www.adgridwork.com/
From the site:
Why use adgridwork...
to advertise your website?
* It's 100% free. Thats right folks: Free Advertising. No payments. Ever.
* Increase your traffic. We have thousands of sites on our network all ready and waiting to freely advertise your website or product.
* We have attractive advertisement blocks AND text links. Most people are blind to the traditional AdSense ads. Our free ads are fresh, simple and appealing to the eye.
* Promote to a targeted audience. You can define exactly what types of sites you want your free advertisement to appear on.
* Registration and setup is a snap. Our service is completely user-friendly.
* Free metrics and tracking tools for webmasters. We provide you with detailed information on the users viewing your advertisements and websites.