You can download Public-domain books online.
Gutenberg.org offers many e-books as txt, pdf, html format.
This is an e-book store and gives away certain copyrighted e-books and digital comics.
The selection is limited but changes all the time.
wowbrary.com you can be member and download some ebooks.
Many libraries also have e-books that you can borrow online.
The Book Depository