Once the thankless workhorses of the Web, search engines are now set to control the most promising form of online advertising yet. A recent report from comScore Network's Media Metrix qSearch tracking system determined that 64 percent of the U.S. Internet users who visit a search engine actually conduct a search on that site. Increased search engine usage has made searching so hot that many analysts are calling it the next killer app. A company pays a fee every time you select its site from the list of search results. It's still early for this form of online advertising. The larger, more established companies have yet to throw their advertising weight around, leaving, the top spots to smaller companies with smaller budgets.