There are four main modes of advertising charge. But they are not effective.

CPM : Cost per Thousand ( M = Roman symbol for 1000 )
It is used by programs that pay on an impression basis -- with the CPM rate being the amount you earn for every 1000 times an advertisement is displayed. For example, a $5 CPM means you earn $5 every time 1000 ads are displayed on your site.

CPC : Cost per Click
This term relates to the amount that will be charged to the website every time someone clicks on their link, for example if the CPC is 5p then the company will be charged 5p whenever someone clicks on the link.

CPL : The cost an advertiser pays per lead. This is a very common method of selling advertising. A lead can be anything from an e-mail address for a newsletter to a complete survey that needs to be completely filled out and verified in order to get credit. CPL prices can range greatly depending on the program.

CPA : Cost per action for banner ads. This is the best type of rate to pay for banner advertisements, and the worst type of rate to charge. Advertisers only pay for the visitors who click on their banner and then sign up, fill out a form, or purchase something on their website. This is most common for Affiliate Programs. My opinion is this type of payment arrangement is already an endangered species, and will soon become extinct.