So, I happen to be a voracious reader, and I find myself constantly looking for ways to find free books and articles. Here are some of the best places that I've found so far:
Project Gutenberg: The first place to look for out of copyright books. It also has some more recent books, including books that are in the creative commons. It focuses on putting books in ePub format for use with eBook readers.
Google Books: A great service from Google. It's primarily has books to purchase, but it has a large collection of free books, mostly books that are not copyright. You can find some really strange, unusual books, such as 16th century anatomy textbooks as boingboing suggests here. Plus, there is a Google Book app for your iPad, iPhone and Android devices to read all the books you find on there.
As I find more resources, I'll post them. Feel free to post you're favorites in the comments.