Heres some info. Tho to be honest. The best idea is to signup to these sites using their minimum deposit free money offers via special links to test whether they are any good (before you spend your own money). Adwords - Probably the best most comprehensive Advertising programme - Millions of potential publishers to show your ads - But is competitive for advertisers - On avg for most keywords is more expensive. - Relevant ads YSM - Less publishers than Adsense - Fewer advertisers - Some gr8 deals/keywords to be found - Not always as good clickthrough->signup/purchase rate as Adsense - Relevant Ads MSN AdCenter - Only currently shows ads on MSN sites (higher quality traffic????) - Less Advertisers than those above - Loads of gr8 deals - Buggy system (that has cost some people money) - Unproven Adbrite - Less publishers/advertisers than the big names - Questions being asked whether it blocks pay-2-click sites in China (click fraud) - Relevant ads - Cheaper - But Quality of traffic??? Bidvertiser - Not relevant ads - Cheaper keywords - Manually and automatically checks for click fraud - Choose specific sites to advertise on - Less publishers/advertisers than those above. Clicksor - Not relevant ads - Question mark over clickfraud - Forces users to click through with captcha to detect automated bot click fraud (but doesnt help for manual click fraud) -Less advertisers/publishers than the big few