Richard Feynman won a Nobel prize for his contributions to physics, particularly quantum electrodynamic theory, and here he gives a series of introductory lectures on the subject. When I try reading articles on Wikipedia about quantum theory I find I often can't get much out of them because they consist entirely of abstract arguments, weird terminology, and bizarre equations, but Feynman has the ability to break things down in a comprehensible way for the layman. He's also just plain fun to listen to.
Quantum electrodynamics describes how electromagnetism works: things like electrical charges, magnetic attraction, and the transmission and reflection of light--everything, as Feynman would say, except for radioactivity and gravity.
He gave these lectures in New Zealand in 1979, the first time he'd tried giving an introductory-level talk on the subject--so he's testing out his presentation methods, and he's charmingly apologetic whenever he has to pause to work out how to proceed. It's useful (and sort of sad) that although this series is over thirty years old, it's still very very close to the current cutting edge of our real understanding of physics.
In the final lecture (#4), he goes on to cover the rest of quantum physics beyond electrodynamics: quarks and all that good stuff, all in his sterling clear and straightforward language.