Here is a New York Times list, no permalink yet. The data are drawn from an automated survey of the top 5000 blogs. Freakonomics, Harry Potter, Blink, and The World is Flat lead the list. Jared Diamond has two in the top ten. Surowiecki’s Wisdom of Crowds is #12. The first work of fiction is The da Vinci Code at #10. Orwell and Narnia are not far behind. I conclude, tentatively, that the blogosphere is increasing the influence of non-fiction books, relative to fiction.
Addendum: Many of you wrote in to suggest that Harry Potter, number two on the list, is a work of fiction. Spending some time with Wikipedia confirmed that this view is probably correct. My apologies for the earlier mistake.