Project Gutenberg is an effort to digitize all books with expired copyrights and provide them to the public free of charge.
To give some examples of the sheer enormity of the project, you can find anything from
the complete poems of Emily Dickinson to
Plato's Laws to books such as
Experiments with Alternate Currents of High Potential and High Frequency by Nikola Tesla. And that's just their English section.
edit: Since I didn't actually recommend anything, I'll do so now and recommend
Flatland: A Romance of Many Dimensions by Edwin Abbott Abbott, just so that you can go around saying you've read a
mathematical satire 