Best ad network?

[fullhdpixel]

I would like to place a small banner on my server to cover my resource-usage. Which ad network would allow me to place ads behind a login screen?

Thanks for your help!

[MentaL]

[Sshadow]

AdHitz[dot]com I know for sure will. Their PPC is kind of low though. However it's better than nothing until you find a better deal.