Seth Godin's Web 2.0 Traffic Watch List is based on traffic to each Web2.0 property. Here is another list of top 200 based on page activity (time spent).
We are excited to announce the creation of the Attention 200â„¢, the two hundred sites that yield the largest share of our attention on the web. The Attention Index is based on the amount of time U.S. internet users spend across the top one million websites. The Compete Attention 200â„¢ represents the best of the best each month.