Project Gutenberg
This post from Norman Walsh reminded me of Project Gutenberg:
Project Gutenberg is the oldest producer of free electronic books (eBooks or etexts) on the Internet. Our collection of more than 12.000 eBooks was produced by hundreds of volunteers. Most of the Project Gutenberg eBooks are older literary works that are in the public domain in the United States. All may be freely downloaded and read, and redistributed for non-commercial use (for complete details, see the license page).
Best of all, all of the books are in plain text, the easiest to manipulate on a computer.