Search algorithms & popularity factors: link, social, click, blog, industry. Since modern search engines are concerned with popularity and not direct relevancy, & big firms up the price of text link buying beyond affordability...
"ShopWiki actively crawls more than 180,000 online stores to ensure you’ll find the products you want at the best prices." For a class looking at web2.0 apps, it's the kind of thing students would enjoy playing with.
