According to Businessinsider.com, here are some of the best and most versatile places on the web to get free reading content for your e-Reader:
Amazon Kindle Store
Google eBookstore
Internet Archive Texts: Texts and Open Library
ManyBooks.net
FeedBooks: Public Domain Books and Original Books
Other notable places to get free eBooks:
Baen Publishing Enterprises
Barnes & Noble's Free Nook Books
Kobo Free eBooks
E-readers come in all shapes and sizes. So which one's right for you? See these five tips for choosing the right e-reader shared by Electronics.howstuffworks.com.