CPM: cost per thousand page impressions.

Blue Lithium
Adagency1
PayPopUp
Barzdo Media
Click Booth
Casale Media  (good for popunders and cmp. hard to get accepted)
CPX Interactive
Gorilla Nation
Real Cast Media
Inter Click
Vibrant Media
Value Click Media  (Decent Popunder rates, cpm, hard to get accepted)
Ad Pepper
Ad Smart
Ampira Media
Adtegrity
Banner Connect
Burst Media (Great for health and beauty. Decent CPMs, Sometimes get direct advertisers.)
Tribal Fusion  (high CPMs but hard to get into, Great pop-under CPMs)
Tacoda
Real Tech Network
Viralytics Media
Morning Falls Network
Turn Ads
Adbrite
Adsense

Right Media (Direct Media Exchange. High CPM. You can set the CPM you get on other networks and they only fill if they beat the CPM you set.)
Value Click
Double Click
Cubics
CPM Bucks
Bidvertiser

Please leave your comments if you know of any good cpm programs that are not listed here.