The major pay-per-click search engine in the US is Yahoo and Google! Search Marketing (previously known as Overture and GoTo), which delivers paid results to many of the major search sites, MSN, AOL, Yahoo! and Lycos included.

Equally important is Google’s Adwords program, which gives you access to the search engine result pages of Google. The Google Adword text ads may also be displayed on web site. If you want to reach as many potential visitors as possible, Yahoo! Search Marketing and Google Adwords will deliver. In Europe Espotting is also important. However, if you want to go for some of the more popular search queries, these search engines can be very expensive.

The smaller PPC services may also be of use. Admittedly, nearly none of them reach any of the major portals, but they do deliver results to a wide array of metasearch engines, and you can get clicks for a very reasonable price indeed.