...a shopping search engine.
Really clever idea, though I think they have a ways to go on the implementation side.
Still, think of the kinds of tie-ins that they can do. If someone searches on Google for a particular brand or model of camera, they can deliver not only the search results, but price comparisons... or maybe even facilitate people to buy the item via online auctioning.
It's probably about the most "evil" thing Google has done yet, really, but it could make them the middlemen in a whole lotta online transactions one day... and they're still delivering their users some very relevant information.