My personal opinion would be
http://www.contextweb.com/ is the next closest to Ad Sense... it's a little different in that you set price per 1000 views and they do the best to fill the ad spots at your set price... if you get low fill ratios you're asking too much... if you get very high fill ratios you're probably not asking enough- it will takes days to figure out where you should be- and it may change over time - such as with xmas shopping ending I expect asking prices will drop.