Pay Per Click (PPC) or Cost Per Action (CPA)
These comprise two of the most cost-effective ways of advertising on the net. In both the options you DO NOT PAY unless someone clicks on your advertisement or takes any other desired action. The benefit of this type of advertising is that in addition to what you pay for, you get free mileage by way of free display of your advertisement.
You may also like one or more of the following options:
Search Engine Marketing (SEM)