The book that I most often wish existed, because co-workers often ask me for it, is a good introduction to object-oriented design.
If you don't care what programming language it uses,
have a serious look at the Inform Designer's Manual,
by Graham Nelson. Skip the first chapters about the
language syntax and go straight
to the section on the object model. (Yes, you can
easily follow the section on the object model
without having read the earlier chapters on syntax;
trust me on this.)
This is without
qualification the *best* computer-technical book I
have ever seen, and it is an *excellent* introduction
to object-oriented programming.
It's not, of course, the only OOP book you will ever
need. After you finish it you will need books that
get down to nuts and bolts in the language you're
going to be using (assuming that isn't Inform).
This is presumably where the books with details
of how Perl OO works would come in.
Nevertheless, as an introduction to OOP in general,
the Designer's Manual is fantastic.
Incidentally, the text of the book is freely
available on the author's website,
so if you want to preview it before purchasing
a copy of the print edition, you can.
The section on the object model starts here, although
the real meat is in
chapter 2, which really can just about stand on its own.
"In adjectives, with the addition of inflectional endings, a changeable long vowel (Qamets or Tsere) in an open, propretonic syllable will reduce to Vocal Shewa. This type of change occurs when the open, pretonic syllable of the masculine singular adjective becomes propretonic with the addition of inflectional endings."
— Pratico & Van Pelt, BBHG, p68