Rules of Play
by Katie Salen and Eric Zimmerman
This is a great general primer to the world of games. It's good for getting things I didn't think of.
Game Feel: A Game Designer's Guide to Virtual Sensation
by Steve Swink
This has been my bible in order to make my game have the proper feel. If the controls fail then the game fails with it.
A Theory of Fun for Game Design
by Raph Koster
Another good primer that makes sure I don't miss anything in the core game. Especially the learned behavior bits.
Creating Emotion in Games: The Craft and Art of Emotioneering
by by David E. Freeman
The game has a story that I'll need to express so it's best that I figure out how to do that well.
Foundation Game Design with Flash
by Rex van der Spuy
This has some good formulas in it.
Beginning Java Game Programming Second Edition
by Johnathan S Harbour
If and when I move to the Iphone I'll be needing this.
Foundation Actionscript 3.0 Animation: Making Things Move!
by Keith Peters
This has some great formulas in it.
Programming Game AI by Example
by Mat Buckland
This was a huge weak point in the first prototype so now I'm going to learn how to do it right.
Behavioral Mathematics for Game AI
by Dave Mark
See above. I love the smell of mathematics in the morning.