"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.
how to refine a topic and its searches; updated for web 2.0 and specialty searching; good for anyone starting to do Internet research on a topic and will take you to some previously unused search tools
The invisible web, or deep web, is estimated to be 500 times bigger than the searchable web and comprises databases and results of specialty search engines that the popular search engines can't index.
You sign up, enter the name of a book, then find out what other folks who liked that book also liked; a tag cloud for the book leads to other books on this topic. Quite addictive, and I just used it to look at the info. around one book.