I have referred to two general categories of search engine marketing: "Pay-per-click" (PPC) services, and Organic search - the "free" listings on the main part of the search results pages.
PPC ads have several advantages:
In some cases, I set up extensive pay-per-click programs, covering a large collection of products. In other cases, we may proceed more cautiously, setting up one adgroup, seeing how well it performs, and fine-tuning it before setting up another.
There are hundreds of PPC sites. Most of them are worthless and many are total rip-offs. The only two worthwhile ones are Google Adwords and Microsoft adCenter, in that order. I usually set up Google and work out all the bugs, then clone it over to MS adCenter if the client wishes. Facebook now runs PPC ads and allows for precise demographic targeting, since Facebook knows so much about its members.
These services syndicate their ads to other sites. For instance, Google Adwords ads are also shown on Ask.com, Netscape, AOL, USA Today, The Washington Post and over 50% of the Media Metrix Top 100 sites that show advertising—sites that reach over 80% of U.S. Internet users.
Next: "Organic" SEO