I hate having to read the manual.
The 'EU in a Nutshell' is a miscellany of facts and anecdotes about the system which rules us. It's a book you can delve into in pursuit of a particular fact, or crack open for entertainment at virtually any page.
Thus, the standard library will serve as both a tool and as a teacher.
I read 'Backstage' a lot when I first was unleashed into the world from drama school. And what was great about it was that if I was using it or not, it was just nice to know what was happening in my community.
I'm not sure what to call 'Lego Star Wars: The Visual Dictionary.' Nonfiction? Movie/toy fiction? But it is any Lego/'Star Wars' kid's dream. Call it spectacular.
Give me a user manual, and I'm happy for hours.
I started by looking everything up in a Star Trek dictionary so I knew what I was talking about, but you can't do that because they talk in circles, and half of it doesn't make sense, so you'll just end up driving yourself more insane.
A reader ought to be able to hold it and become familiar with its organized contents and make it a mind's manageable companion.
The Prydain Companion is more than a quick reference or handy glossary, though it is all of that as well. Instructive, certainly. But, like any good companion, a pleasure to be with over a long period of time.
The QSM Software Almanac is an invaluable resource. It establishes a norm for software projects, including best of class, worst of class and averages. In addition, it profiles the state of the art of software construction and enhancement. I wish I'd had this wonderful reference book years ago.