Kitaab At-Tawheed - Ibn Abd al Wahhab's "The Book of Tawheed" - translated as an online book by Sameh Strauch. - http://islamicweb.com/beliefs/creed/abdulwahab/
Ibn Abd Al-Wahhab, Muhammed - Biography (1703-1792); also includes an account of his later influence. Article on Wikipedia. - http://en.wikipedia.org/wiki/Muhammad_ibn_Abd_al_Wahhab