Hungarian Method

Easy to understand examples:

http://www.ee.oulu.fi/~mpa/matreng/eem1_2-1.htm

http://www.ams.jhu.edu/~castello/362/Handouts/hungarian.pdf

http://www.public.iastate.edu/~ddoty/HungarianAlgorithm.html

animation: http://www.ifors.ms.unimelb.edu.au/tutorial/hungarian/index.html

topcoder tutorial: Assignment Problem and Hungarian Algorithm (very good regarding theory and c++ code)

http://www.math.uwo.ca/~mdawes/courses/344/kuhn-munkres.pdf