Shopping, the biggest source of traffic is probably still general-purpose Web searches. Otherwise, make sure to do this yourself. Don't expect your site to show up in search engines immediately. It will show up in AltaVista in a couple days, but most other search engines are slow to add new listings. Some only seem to rebuild their databases every couple months.
Most search engines filter out sites that try that.
The best approach is to use key words frequently in your site, but not in a way that appears unnatural. For example, Vitanet is a site selling dietary supplements. The purpose is not only to sell the product, but to draw hits from search engines. The more text in your site, the bigger a target you present to search engines. One thing not to do, if you want traffic from search engines, is use software that generates your pages dynamically.