There are a lot of books that GMs can use to make their game better. Tonight I am going to highlight five of my favorites, and give a couple of honorable mentions. My game is a megadungeon, so that may influence this list. Here it is, with a few words on each:
5. The Name Book, by Dorothy Astoria (1992, 1997). It's simply a list of 10,000 names in alphabetical order. When I need a name, there is always one close at hand with this book. Pretty much any name book will do. Nothing is worse than Barkeep #12, so avoid that with a book you can find at a flea market or garage sale for less than a dollar.
Frog God Games) is a great resource for when the player-characters get out of control. He expertly explains how to bleed gold, resources, time, or anything else they might stack up too much of. And he makes sure the players still have fun! The PDF can be bought for $5 at the link to Frog God Games.
Goodman Games (2017 - It may not be available at retail yet) This book contains advice from a lot of great designers: Jim Ward, Christopher Clark, Skip Williams and Brendan LaSalle to name a few. They cover a huge range of topics, from context to description. It's going to be $30 when you can get it. It is worth it.
Frog God . This book literally walks you through creating adventures. It has charts upon charts (and what self-respecting GM doesn't love charts?) with everything from location names, to types of clues, and
special effects for teleportation devices. It is basically the 1E DMG on steroids. It's going to set you back $21 on PDF or double that for print. Every time I am working on a dungeon, I pull out this book.
I'm not going to go into detail with my special mentions, but I think they are noteworthy. Someday, they may even get their own post. Here's 3 more books to be on the look out for:
Special Mention #1: Storyteller's Thesaurus by James Ward and Anne K. Brown
Special Mention #2: The Dungeon Alphabet by Michael Curtis
Special Mention #3: The Random Esoteric Creature Generator by James Raggi
Hunt them down. You will be glad to have them all in your collection.