10 year history of internet advertising
If you are interested in seeing how web advertising has changed over the past 10 years, or if you would like to better understand what the state of the web advertising world is today, then this is a good report to read:
The decade in online advertising
How Web Advertising Works
This article (written perhaps 3 years ago) is now a bit dated in terms of ad rates (they've gone up since the article was written), but still provides a nice overview.