Adsense is the best ad network for blogs and forums. Adsense offers two kinds of ads CPM and CPC. With CPM, you earn from ad impression and with CPC, you earn for every legitimate clicks. However, you are likely to earn more with CPC ads, if the clicks are legitimate. CPC stands for Cost Per Click, where publishers earn 68 percent of the revenue generated by their webpages. In other words for every $1 spent by the advertiser, publisher earns 68 cents. CPM stands for Cost Per Millie, where Millie stands for one thousands. You will earn fixed amont per 1000 ad impression.