I'll start with one of my top half dozen favourite novels - Nineteen Eight-Four. There have been dozens of paperback editions since it was first published in 1949, with Penguin leading the way. Here are three editions from Penguin - the first from 1954, an imaginative reworking from 2013 and a Times promotion from 2009.
Penguin 978 - 1954
Penguin 978 back
Penguin - 2013
Penguin - 2013 - back
Penguin - 2009
Penguin - 2009 - back