Eats, Shoots  &  Leaves: The Zero Tolerance Approach to Punctuation - Lynee Truss
Not a reference book as such, but a humourous guide to the modern use of punctuation and why it is so important to maintain standards without being too rigid.Highly entertaining and education; I will be keeping two copies by both my work computer and my home computer just in case I am tempted to stray from the rules.