What is a good reference book for cabinetmaking and/or other millwork?
There are libraries of reference material out there so I'll just give you three that are suitable for beginner, intermediate, and advanced. When I say "advanced" I don't mean that you are an advanced woodworker, but that you have a desire to get a little deeper into the theory and underlying concepts than someone that's just trying to bang together some cabinets.


Beginner: Building Kitchen Cabinets (Taunton Press)

Taunton Press has released dozens of reference manuals covering everything from traditional joinery to building your own work bench and even one specific to cabinet making. They have great full color pictures and illustrations and cover a pretty solid base of information in clear simple language, but anyone with carpentry experience and a desire to get to the heart of things will feel like their only getting a skim coat. 
Intermediate: The Encyclopedia of Furniture Making (Ernest Joyce)

This is the "Codex Gigas" of woodworking. It will teach you everything you want to know about furniture and cabinet making you ever wanted to know (and probably more) but it is entirely focused on techniques, methods, and mathematics in the dry delivery of a scientific text book. Also it was written in 1970 so some of the tools and techniques are less than cutting edge.
Advanced: Anything by James Krenov (specifically The Fine Art of Cabinet Making or The Impractical Cabinet Maker)

James Krenov's books are probably the finest written material on the subject of woodworking (and craftsmanship in general) ever committed to paper. They not only cover a myriad of great techniques and practices, procedures and processes, methods and methodologies, but also delve into the softer side of cabinet and furniture. He discusses design, stock selection, the soul of the work in a way that's approachable even to people that wouldn't consider themselves artistic or creative. And at least for me personally, his words on how to think like a craftsman were nothing short of inspirational.


Now, these are all good reads and worth owning for anyone into woodworking. But honestly the best way to learn a trade is to watch someone doing it. Youtube, surprisingly, has a great wealth of videos with everything from garage jockeys talking about their latest successes and failures to the entire library of This Old House and The New Yankee Workshop. Some of the content is more...accurate.. than others but it's actually a pretty effective learning tool. And if you like the Stack Exchange format, there's a Woodworking Community in the commitment phase as we speak so please consider signing up!!