A site map should be present at every web site. They are not sexy or fun, but they are a staple of an effective navigation scheme.
A site map offers visual representation of the information space in order to help users understand where they can go. Site maps are as old as the Internet, but new research shows they still play a valuable role for site users.
Jakob Nielsen recently published the results of two research studies conducted to find out how people use site maps. The results showed that site maps are still useful as a secondary navigation aide, and that techniques and usability have improved over time.
See the full report at: http://www.useit.com/alertbox/sitemaps.html