There is an article in Sunday's New York Times about virtual book kiosks placed online by the British Library and the Museum of Modern Art.
One of the British Library books now online is the Lindisfarne Gospels, written and decorated in the VIII century, while MoMA-Queens has a few books from their 2002 exhibition, The Russian Avant Garde Book: 1910-1934.
See also the first two Caxton editions of The Canterbury Tales at the British Library site. Very nicely done, showing the type very well and even, remarkably, giving a good sense of the qualities of the printing.
If you ever get to the British Library, you can pick up CDs of the various books featured in their kiosks. I've had the Lindisfarne Gospels CD for a few years, and it is a real treat to flip through.
Captured from web.archive.org on 11 Oct 2013. view this capture