My favorite book on statecharts is "Real Time UML" by Bruce Powel Douglass. Bruce worked directly with the original creator of statecharts, David Harel. His book spends a lot of time talking about why you would do something in a statechart, not just what the diagrams mean. He also explains several other UML concepts very well. He talks a lot about embedded considerations like timing contraints which may not be very useful in your application.
Another good book on state charts is "Practical Statecharts in C/C++". The main purpose of the book is too explain the author's implementation of statecharts, so you get a lot of discussion of the low level details of how a statechart works.
Tony Gray
