One of my favourite series of books, in both content and design, are the Penguin Modern Classics. They've been around in one form or another since the middle of last century, and I'll be looking at the earlier versions in a later post.
Since the 1990s, however, they have had several redesigns, illustrated in this photo (click for a larger view).
1.) This is a Penguin Twentieth-Century Classic (as they were known for a while), with the characteristic blue-green spine, non-orange Penguin Logo, and white cover/title text box. This was the look from the 1990s, although some books are still in print in this format today, not having yet been updated.
2.) In 2000, Penguin hired designer Jamie Keenan to redesign the Twentieth-Century Classics, and restored the original Penguin Modern Classics name. The spines became silver, with the author/title text limited to a narrow silver band on the cover. This meant that the unobstructed cover image took up the majority of the cover--usually rather effectively.
3.) In 2004, this design was slightly altered by the addition of a white band containing the Penguin logo and the words 'MODERN CLASSICS', bringing the Modern Classics into line with the 2001 redesign of the "black" classics (see the Phil Hale covers for the Joseph Conrad books for an example of these).
4.) Starting in September 2007, the Modern Classics have undergone probably their most substantial redesign ever. The spines are now white (matched by narrow white bands at the top and bottom of the front cover), and the restrained text has turned into huge silver and white lettering which obscures a large chunk of the image. I was not at all sure about this to start with, but it can be very effective: look at these lovely covers for two collections of the great Eileen Chang's stories and novellas, to be released in December this year.