Math Physics and Engineering Applets (an impressive collection of applet/simulations, these are a little less intuitive than PheT, but cover a lot more quantum ideas)
Mathematica Integrator This is an online integrator, just type in your indefinite integral (in Mathematica's syntax, of course).
Stern-Gerlach apparatus A simulation of a device to measure spin 1/2, possibly the simplest (and most instructive!) quantum mechanics problem of all