An historical reference, along with a solution and interesting links for the Konigsberg bridge problem is found at this site: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 provides a thorough overview of the Traveling Salesperson Problem (TSP):
http://www.nist.gov/dads/HTML/travelingSalesman.html
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