Combinatorics Websites:
emathlab.com
eMathLab - Math Help - Math Skills - Math Practice
Math skills practice site. Basic math, GED, algebra, geometry, statistics, trigonometry and calculus practice problems are available with instant feedback.
orthuber.com
The Recombination Principle: Mathematics of decision and perception (index.htm)
Mathematics and physics of our decision and perception (recognition) process (not without connection to ethical and philosophical aspects)