Pop-ups and downs are normally the best paid ads. But there are 2 problems with those advertisments: Users can find them very annoying and because of that, many people are using pop-up blocker to avoid them.

Clicksor

Details:
Clicksor pays you every 2 weeks per paypal, if you reach the minimum payout of 50 $.

AdultAdworld
http://www.adultadworld.com/
Details:
Here you can monetize your Adult-Website-Traffic!
You will get paid 1x per month after reaching at least 50 $.