CPM ads are the ad earning ads that many ad networks run for publishers, when they are viewed, these are called impressions and these if your traffic flow is quite high for your website or blog, then the more impressions you get, the more revenue is generated, most ad networks combine different ratios with CPA and that is Cost Per Aquisition which is really just what converts, a lead or a sale.

Cost per 1000 impressions is the usual standard for a CPM, but varying ad networks adjust this to their own preferences

Adsense uses the cpm and cpa model for it's adsense publishers and this works quite well, if you have alot of traffic going for your site.

Affiliate cpm's are also available in the affiliate networks, so seek them out.

Try out Pepperjam Affiliate Network - It's a rising affiliate network with some good conversions.