Well a good content supplier would depend on what is the theme of your site. We do teens and the good stuff is in
www.paulmarkham.com how good are we? Is this good.
As for everyone and their brother buying from Matrix, what does that tell you? The surfer likes their stuff and comes back to see more or he never signs up?
Under used content is usually under used for a reason, it's crap and the sites buying it do not survive and prosper.
Also try
www.photorama.nl
www.adultstockphoto.com
www.glamourgirls.biz
*edit*
Just took a look at your site and we are not what you want, unless you have a teen site. The first two will have what you want. Tell them Paul Markham sent you.