Penguin Australia are about to release a series of 50 books they're calling 'Popular Penguins', all of which use a modified version of the original Penguin design from 1935--the famous 'horizontal grid' devised by Edward Young.
Unfortunately, as you can see here, they're making them all orange (the colour originally used just for fiction), rather than using the various other colours to denote genre (such as green for crime, maroon for travel, blue for non-fiction, etc).
You get the idea. This latest series of Penguins means that they have up to five different editions of some books, like Pride and Prejudice, out simultaneously (and even more if you count their subsidary companies like Signet and Dorling-Kindersley). Even throwaway fluff like Donna Tartt's The Secret History is available in three editions now. Bizarre.
The best retro use of that horizontal grid, though, has to be the cover of Penguin by Design, Phil Baines' fascinating 2005 history of Penguin covers. This cover was designed by the great David Pearson.
Here's the full cover: front, back, spine and flaps. It's clever and beautiful (and printed on really nice paper stock, too). Click for a bigger version.
And, just for the hell of it, here's a double-page spread from inside the book, showing a bunch of Penguin crime novels, many designed by Romek Marber. Again, click!