Not totally up-to-date as far as the more recent years go (e.g., 2002), but interesting for the historical content, or something like that. 1981’s bestselling novel was by James Clavell, and the bestselling non-fiction book was a diet book. 1919’s bestselling novel was The Four Horsemen of the Apocalypse, by V. Blasco Ibanez (which, if you’re interested, you can read thanks to Project Gutenberg).
Bestselling info from Publisher’s Weekly, and hosted web-side by Publisher’s Lunch.