Well – I think this project is so big and famous, it hardly needs to be mentioned. But to continue our series on Free Culture (as in speech and/or beer), I’d like to point you to Project Gutenberg, which endeavours to make public domain books available for free in ascii and html format. These are not just amateur books; works published by Project Gutenberg include books by such greats as Burroughs (Tarzan), Doyle (Sherlock Holmes), and others.
This works especially well if you carry a PDA anyway. I used to read many of these books, way back when I had a Palm III. Good times. (Ironically, this is the best use I ever found for a Palmpilot – possibly with the exception of Metro – which in itself is quite revealing.)