Best CPM Affiliate Network?

I have a few sites that get decent traffic, they have to do with free downloads, so usually people ignore most everything else and are just trying to download what they are looking for. Because of this I have found CPA offers on my skyscraper sections and PPC ads don't really do to well, or pay to low. So I think what would be best is to try out some PPV/CPM ad network, where at least I can make a little extra income from the views I get anyway. I have never used a CPM view based network so I'm not really sure what all are the good ones, any recommendations ?

anyone know about this?

I would be very interested in hearing some opinions on this too.

Here you go :

madadsmedia.com
tribalfusion.com
pulsepoint.com
valueclickmedia.com