The MIT Press offers open access to some of their books, allowing anyone to read them for free. Although I knew about OpenCourseWare and that books like SICP were freely available, I wasn't aware of just how much they offer.
The fact that a book is freely available might not be immediately apparent. In his post on software safety, Hillel Wayne mentions a book and says, "In the lower-left sidebar there’s an option to download the book for free. Most people miss that." Even seeing this message, it took a minute to find the download link – it's now behind the Open Access tab.
Some books are available as a single PDF which I prefer over the others that are often a collection of PDFs or HTML files. It takes a couple clicks to see if the book is a big PDF, and then the back button would take me all the way back to the first page.
Publishing these books for free is a tremendously generous act, but I was slightly frustrated by the website. I gathered all the direct links on a single page for quick browsing. Check out all the open access books from MIT Press.