Sundial Calculator for Windows
"Astronomical Algorithms" by Jean Meeus - Willmann Bell Publisher (very good)
"SunDials Their Theory and Construction" Alberrt Waugh - Dover
"SunDials Their Their Construction and Use" R.Newton Mayall & Margaret W. Mayall - Dover
"SunDials History, Theory and Practice" by Rene' R. J. Rohr - Dover (very good)
"Easy to Make Wooden Sundials" by Milton Stoneman - Dover
British Sundial Society
All great books on the subject matter.
Willmann-Bell and Dover are both great publishers for the Amateur Astronomer and Scientist.