Project Gutenberg - Free ebooks in your language of choice
Project Gutenberg is a library of free ebooks, focusing on older works whose copyright has expired and which are now in the public domain. While you won't find any recent releases here, it's a good source for reading the classics.
They have categorized the books by publication language, so you can find books in the language of your choice. Most of the ebooks are available in a choice of formats such as "epub" which are likely to be compatible with any e-reader app on your phone or other device.