Quantum Mechanics Tutorial http://www.gilestv.com/tutorials/quantum.html This cool tutorial is one of the Flash-animated Modern Physics Tutorials by Giles Hogben. Extensively illustrated, this tutorial probes questions such as wave-particle duality and offers a good general introduction to quantum physics.
Grains of Mystique: Quantum Physics for the Layman http://www.faqs.org/docs/qp This site provides good historical and experimental background info - and they've documented their sources and made some attempts at peer review.
Quantum Physics Online Version 2.0 http://www.quantum-physics.polytechnique.fr/index.html This is a cool set of programs that run in your browser, giving simulations of various quantum physics experiments. Look for info on wave mechanics, quantization, quantum superposition, and spin 1/2.