Some of the material in this chapter was inspired by the Learn My Language page from the Los Alamos National Lab
There's a good article on finite state machines at http://www.i-programmer.info/babbages-bag/223-finite-state-machines.html
Textbooks on formal languages will have considerably more advanced material and more mathematical rigour than could be expected at High School level, but for students who really want to read more, a popular book is "Introduction to the Theory of Computation" by Michael Sipser.
Regular expressions and their relationship with FSAs is explained well in the book "Algorithms" by Robert Sedgewick.