Amazon's A9.com search portal is cool
A9.com maintains a search history and is especially nice when search results are from inside a book - you can often read relevant pages out of books. A9.com uses Google, the internet movie database, the amazon.com database, and other information sources.
I have been using the Google SOAP web services API for about 18 months - very cool to be able to use Google easily in my own programs. I would like to see Amazon offer something similar. Amazon does have both a SOAP and a REST API for accessing its main site, but I don't think that this is tied in with their search site yet.