Here's a 40 year old dust jacket I stole from the library's donations bin. I love the subtle things time does to paper. The softness of the letters, the variations in the colors, the unifying texture and color of it.
Penguin books are always well designed. Including the Pelican series.
In the 60s.
And today.
Chuck Palahniuk books tend to be well designed.
Such awesome book design. Can't find any images of the back or spine which are just as cool. If you can't see, the negative space of the letters is naked chicks. My kinda' design.
Michael Chabon's books are also frequently well designed
The Library of Congress has a flickr account! Thousands of free public domain images ftw! Amazing stuff. Great reference and great for web use. They only catch is that for now they've only got 1930-40s New Deal type stuff and 1910s news shots. Hopefully they'll add more.