I use a variety of ad networks on my site, ranging from CPM (Burst Media, Fastclick, Casale Media) to CPC (AdSense), but I try to limit the amount of advertising so it doesn't detract from the site.

Although it is noble to make a site which loses money, I'm a university student in the UK, which makes me pretty skint. I couldn't actually afford to run a site which lost a lot of money. I don't mind if they just break even though.

Regards,

Tim