On the actual proxy page: AdSense AdBrite AdVersal Those are the main ones people use. Just google "cpm companies" - 90% of them allow it to be on the proxy. HOWEVER, on the proxified pages, it is against a lot of sites' TOS to place CPM ads on. This is, including AdSense.
Ummm, They do pay CPM though. Aversal pays CPM Adsense pays CPC and CPM (depending if you have site targeted advertisers or not.) Adbrite also pays CPM I believe.
Not many of the well-known CPM companies out there that ForgottenCreature noted accept proxies. Try CPX Interactive, they're fairly lenient on the types of sites they allow.
I think you should worry first about which CPM networks accept proxy sites, and later which one is the best. As it is, the best CPM networks do not accept proxy sites.
They used to be, not anymore, look in the affiliates section and see how many people crying foul over not getting accepted to CPX.
me too was looking CPM ads to put on my proxified pages. ps. i have try, adbrite, adversal, canepmedia, freedomads. but i wasnt satisfied with their rate.