On the topic of pretty covers, I love the covers of these two books a lot:

1. The Art of the Metaobject Protocol (https://mitpress.mit.edu/books/art-metaobject-protocol)

2. The Art of Prolog (https://www.amazon.com/Art-Prolog-Second-Programming-Techniq...)

but haven't been able to find any other motivation to buy them. Also I have never printed the Common Lisp Quick Reference(http://clqr.boundp.org/clqr-a4-booklet-all.pdf) because I always imagine it having a really pretty cover, and everything I try just falls short.