One of the things I vainly enjoy about e-books is that I can choose my favorite covers and apply them to whichever edition of the book I happen to have. The cover of a book sets its mood, and browsing through these covers in the Calibre grid offers remembered fragments of the worlds within.
For Joseph Conrad’s Heart of Darkness I use the Vintage Classics cover, slightly modified.
For Trevanian’s Shibumi I use the French Gallmeister cover.
For Douglas Adams’ Hitchhiker’s series I use illustrations by Wayne Dorrington (unfortunately missing the last two).
For Uncle Bill’s Sprawl trilogy I use covers that were previously used by Editora Aleph for the Brazilian editions.
For Gibson’s Bridge and Blue Ant trilogies I use the Penguin covers.
For Burning Chrome I use Daniel Brown’s fractal cover for Gollancz.
I don’t recall where I acquired the cover for my omnibus The Lord of the Rings.
Sometimes the editions I purchase come with enjoyable covers. I have a few of William Scott Wilson’s translations of historical Japanese works, and I find the covers used for his books by Shambala Publications aesthetically pleasing.