Either (e)CPM or CPC. I have an account with advertising.com, but I'm not currently using it. They actually provide direct sale (commission based) as well, last I checked. Mostly it's CPC though.
If it's CPC then that site must be raking in tens of thousands of dollars. Their stats say that they get over 10 Mil visits per day. I guess this is a good alternative to adsense too? Fsmedia - if you ever use your account, let us know if it can compete with adsense.