The free online encyclopedia has quite a few articles dealing with quantum mechanics. As an example, have a look at the description of the hydrogen atom:
Incidentally, the picture of the orbitals was created by myself, a long time ago. It is amazing to see how much the page has changed since then. With pictures that is no problem (they usually stay intact as a whole), but with content that’s another story. I have mixed feelings about Wikipedia (and currently do not contribute any more), since the content can so easily be degraded by some (potentially well-meaning) incompetent beginner (sorry to be so blunt).
That being said, Wikipedia is still a great resource (if used with care) and an amazing phenomenon!