Here are more (dangerous) websites where you can find previews for art related books.

• Nucleus | Art Gallery and Store
• Nattoli's blog
• Book By Its Cover
• The Designer's Review of Books
• Fantagraphics Flickr photostream
• Design Studio Press
• Ballistic Publishing
• CQコミックスタジオ

And there's also Creative Uncut's gallery, which features the art but not books.

If you know of others, share them via the comments.