This is an incredibly generous endeavor by Caltech: they have published The Feynman Lectures on Physics in HTML format, available for free:
Caltech and The Feynman Lectures Website are pleased to present this online edition of The Feynman Lectures on Physics. Now, anyone with internet access and a web browser can enjoy reading a high-quality up-to-date copy of Feynman’s legendary lectures. This edition has been designed for ease of reading on devices of any size or shape; text, figures and equations can all be zoomed without degradation.
Get your fix of Volume I.
1) If you’re wondering, the hardcover set of the lectures goes for around $180 on Amazon.