I was recently directed to ManyBooks.net as a good site for free books. There are a lot of the Project Gutenberg books here, but the layout and organisation is much better, and books are available in many popular eBook formats, including my preferred PalmReader (pdb) format. I'm a long time fan of the late Robert Heinlein, and given his many references to Edgar Rice Burrough's John Carter of Mars series, I've always wanted to read them. So it was a nice surprise when I found book one of the series, Princess of Mars. Books two to five are also available.