BlogPulse

BlogPulse is a service that scans blogs, to see trends in what people are writing about.

one application allows you to see how a new thought or trend becomes popular by how many people are writing about it in their blogs. Remember that there are now >9m blogs in the world, and that the largest blog hosting service, Blogger, gets more daily page views than the New York Times online. Inclusion in a blog is a very valid way of seeing people, ideas, and brands rise and fall in society.

Some examples -

Joseph Ratzinger

The Long Tail

adidas Vs. Nike Vs. Reebok

Thanks to Scott for the tip

This is a free service at the moment, but I'm guessing it won't be for long!