For basic straight razor history (when certian materials were used for scales, certian stamps or steels used) these are good:
The Standard Guide to Razors by Roy Ritchie (Author) , Ron Stewart (Author)
ISBN-13: 978-0891456582

Straight Razor Collecting: An Illustrated History and Price Guide ISBN-13: 978-0891451266

For anything more specific, you may need to focus on a particular area such as Sheffiled or Solingen (SP?)

Best of luck!