[Hofstadter 99] Hofstadter, Douglas R. Göodel, Escher, Bach: An Eternal Golden Braid, Twentieth Anniversary Edition.
[Stein 97] Stein, Lincoln D. How to Set Up and Maintain a Web Site, Second Edition. One of the best books written about creating and maintaining a web site.
The official Apache SSI page: httpd.apache.org/docs/howto/ssil
An extensive tutorial from Bignosebird.com: www.bignosebird.com/ssi.l
A tutorial from the folks at NCSA: hoohoo.ncsa.uiuc.edu/docs/tutorials/includesl