I've been having great results with
Cams.com. I'm getting a 1:250 ratio. The trick to cams is to promote the models ad their services, not the site. So Ordinary banners with cam advertising doesn't do it for me. But Lot's of images and model profiles and links to the camsites, that works great for me
As an alternative to
cams.com you could try
AWE or
Payserve