Best 3D Engine Reference Book?

Horizon_99 asks: "This is more of an ask John Carmack type question but since he already did this I would like to ask the community what is in your opinion *the* reference book to 3d engine design? And I don't mean a directx for dummies type book but something more along the lines of the physics related to 3d environments and such. Where should I invest my hard earned money for this part-time hobby of mine?"