Professor David Friedman has a good history of digital cash in his book "Future Imperfect" - the chapter can be found here: http://www.daviddfriedman.com/Future_Imperfect/Chapter6.html
(minor nit: Friedman thought Chaum was Dutch).
The link to the back story on what happened to DigiCash is worth putting:
http://cryptome.org/jya/digicrash.htm
(and yes, I realize Ian Grigg found the link)