Key factors to condider when designing a navigation system or user interace:

Develop a grid to follow a consistent layout for global and local navigation.

—Organize global and local navigation according to hierarchical systems.

—Create navigation for large subsets such as drop down menus or search tools

—Create an online environment that takes into account user response.

—Organize and structure navigation to have immediate access to key data.

—Understand your most important message and have navigation support it.

—Offer variable opportunities to get to the same place.

—Be sensitive to your virtual environment, keeping the user housed within your site.

—Keep navigation devices consistent.

—Be appropriate when developing an "experienced" model of navigation.

Grid
http://www.cjprecision.com/

Interesting or entertaining navigation
http://www.dicksons.com/
http://www.tmbg.com/
http://www.fork.de/v4.1/?page=contact
http://www.methodologie.com
http://www.limn.com/ (navigation changes from retail to magazine)
http://www.benetton.com/colors/
http://www.bbkstudio.com

Detailed navigation
http://www.fork.de

Creating sub-rooms for navigation
http://www.futurefarmers.com/
http://www.ushmm.org

User response such as sound or roll-overs
http://www.digitas.com/
http://www.hermanmiller.com/
http://www.oddflavor.com/
http://www.angrymonkey.com/site01/
http://www.aptargroup.com/markets.asp
http://www.bmwusa.com/welcome.cfm?code=Home

Various ways to navigate
http://www.angrymonkey.com/
http://www.ideo.com/about.htm

Sites with searching capabilities
http://metmuseum.org/
http://www.burton.com/

Lower navigation bar
http://www.lhsysnet.com/_fr_select.htm

Navigation Advice

http://www.useit.com/alertbox/20000109.html