An historical reference, along with a solution and interesting links for the Konigsberg bridge problem is found at this site:

http://mathforum.org/isaac/problems/bridgesol1.html

This site from Math 103 at the University of Alabama provides a nice overview of Euler circuits and Hamilton cycles. Click on the topic in the left column.

http://www.ctl.ua.edu/math103/

This site provides a thorough overview of the Traveling Salesperson Problem (TSP):

http://www.nist.gov/dads/HTML/travelingSalesman.html

This site provides a TSP problem solver:

http://home.hiwaay.net/~kdunn/problems/tsp.shtml

This site, by Chris Caldwell provides Graph Theory tutorials:

http://www.utm.edu/departments/math/graph/

An interesting site about Mobius strips is found at this site:

http://mathforum.org/sum95/math_and/moebius/moebius.html