First off, check out these awesome redesigns of the Harry Potter series! M. S. Corley designed these inspired by both Moss and Spacesick, and retro Penguin covers in general. All the covers make sense with their plots, and yet feel so retro; I did a double take at first—”Harry Potter’s not that old, is it?”.
Next up, I’m super bummed I only found out about these a year and a half after they were released. Puffin Classics (the Penguin children’s division) had six famous architects including Frank Gehry design children’s book covers to celebrate their 70th anniversary. The titles include James and the Giant Peach, Little Women, Treasure Island, Oliver Twist, Around the World in 80 Days and The Secret Garden. Check out the website for more details (UPDATE: the Puffin Classics link no longer works, but you can find more details in this article from Vogue).