If you have an e-book reader, there are many sources of free e-books & audiobooks to download to your device. Here are a few of them:

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Google E-Bookstore - Free ebook selections compatible with many devices
Open Library - Over 1,000,000 Free eBooks & more added all the time!
InkMesh - A search engine that searches more than thirty online sources for free e-books
Baen Books - Over 120 Science fiction and fantasy titles available, with new titles added every month.
Internet Archive - Films, books, music & texts in many downloadable formats
Project Gutenberg - Project Gutenberg makes ebooks and e-audiobooks available for some of the same great literature available in plain text.
ManyBooks - Includes Project Gutenberg titles and beyond.
Feedbooks - "A place to discover and publish ebooks"
LibriVox E-audiobooks in the Public Domain
Literal Systems -"Audiobooks you just can't buy"
The Online Books Page University of Pennsylvania offers an index of hundreds of thousands of online books freely readable
EBook Fling - Swap ebooks for free with other readers nationwide while still retaining ownership!
The Spoken Alexandria Project - free Creative Commons library of spoken word recordings, consisting of classics in the public domain and modern works.