These days, most search engines and directories have a Pay For Performance (PFP) or Pay Per Click (PPC) element to them. These paid services are a way of promoting your site by paying for the extra exposure, rather than relying solely on your site's Search engine ranking as determined by the search engine compatibility of your site design.
The extra exposure can include having your site listed above the normal search listings under "sponsored matches" or "featured listings", or via specially designed text ads that display when your target keywords or phrases are searched on. If you don't have search engine compatible sites, or that don't have the time or budget to implement a traditional search engine optimization campaign to obtain high ranking, PPC options can be good solutions to increasing site traffic quickly. These options are also an excellent choice when used in combination with a search engine optimization campaign to achieve maximum exposure and larger traffic volumes.