Amazon.com sells search results
"Sponsored Results allows anyone to promote a product to our more than 25 million customers. Whether you're an author, publisher, musician, record label, manufacturer, or distributor, you can place your product in a "Slot" in the left column of our search results pages--starting for as little as a penny per impression"

02/09/01 update: Yahoo! now has sponsored sites too.

08/02/01 update: Just discovered this comment about my post. It's interesting to see my headline had negative undertones. I don't remember when I posted this link and quote, but I don't think I had a negative opinion at the time (or I would have commented). Yes it's point-of-sale advertising and cross-merchanding. It's funny, I even had read that study before.

02/15/02 update: Amazon.com: "We have recently decided to stop accepting orders for points and no new Sponsored Results accounts can be opened."