I'm a big fan of e-books. I'm also a packrat, so anytime someone offers free e-books, I'm all over it like butter on toast. So, when I discovered a company giving away free PDF e-books, I was very happy.
Most of the books are classics, public domain stuff. But, they do have a selection more modern writing (Phillip K Dick, Heinlein, Kurt Vonnegut), and a collection of physics textbooks also, including:
* Discover Physics
* Newtonian Physics
* Electricity And Magnetism
* Conservation Laws
* The Modern Revolution In Physics
They made all their books free by tossing in a one-page advertising spread, like in a magazine, every 20 pages or so. There's no encryption, no DRM or anything. They just slap a watermark onto the pages, so they'll know whose account is passing the books around if they show up on P2P sites.
The company is called Wowio, for those who are interested.