I’ve added a link to Joseph Sullivan’s blog about cover design, and it’s also worth noting Cover Design Issues. While these deal mainly with US trade publishing with a bias towards fiction, there are interesting comments on the development of a design, and also you can compare a designer’s intentions with the finished product. They are good at comparing US and UK approaches to the same titles, too.
And if you like design from the 50s onwards, here’s a relaxing place to go.
