NB. The following covers have been collected from numerous places on the Internet. If you find some of your own, and if this offends your personal sense of property or legal copyright, let me know and I will remove them as soon as possible. These covers are collected here neither for profit nor for research purposes but entirely for fun.
Penguin Centennial editions
Penguin Modern Classics
Penguin Classics 1990s/2000s
[The laziest series switch ever!]
Penguin Twentieth-century Classics
Various Other Series