Google's toolbar and content modification
Dave Winer, who im not usually a huge fan of, has a wonderful summation of the arguments against Googles ham fisted attempted to resurrect Smart Tags - among many other great points he says it's adware. I agree.
Even when they link to their map site it's promoting a Google service, which may not, at this time, contain ads, but certainly will at some point in the future. And the map service leads to other Google services that do have ads. So they are using other people's content to make money, money they don't share with the authors or publishers.
When they link from an ISBN to a book page on Amazon, the commercial adware connection is even more obvious.