The Feynman Lectures on Physics probably constitute the most famous introductory physics textbook ever written. The level of intuition it provides is hard to beat; I first started reading it in middle school, and a decade later I'm still finding new insights in it. Yet when I recommend it to others, they often have sticker-shock. It is a three-volume book, after all.
So is there any legal way to read the Feynman Lectures for free, on the Internet?
The publishers of the Feynman Lectures recently released a free online edition! See this link. This should prove an invaluable resource for physics students.
One note for Feynman Lectures purists like myself: the content is of course the same as the original books, but the look and feel of this edition is very different from the original. The font has been changed for easier online readability, the equations have been retyped in Latex, and the diagrams have been redrawn.