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.
Oh, we used the Art of Prolog in my sw engineering course. It's a good book, although it doesn't cover the newer features of Prolog interpreters, like Constraint Logic Programming, IIRC.