comparison shopping engine
Shopping search engines that compare the prices on searched-for products at various online stores. While most comparison-shopping engines do not offer the merchandise themselves, some may earn commissions when users follow the links in the search results and make a purchase from the online vendor.
See "How Affiliate Marketing Works" in the "Did You Know..." section of Webopedia.
Also see Refer-It.com, a directory of referral & affiliate programs for e-commerce, featuring information on over 6,500 affiliate programs.