I've always liked the earlier covers and book-jackets of Penguin. There are several reasons that explain this taste. Among them, these three ones: Limited use of the colors of printing, basic and grim fonts for the tittles and credits, and great, funny -though sometimes a little dry- illustrations containing an unsettling message. they have a british and primitive style really, and discard information that can mislead the buyer. Penguin is the perfect gentleman.
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Well, in this link you have a heck of a Penguin covers: none other than 776 images!