Carlos BenÃtez over at etnassoft has put together a comprehensive collection of mostly open and free books that you can browse and download for free.
He has collected in one easily searchable and browsable site over 2500 books, with titles on technical issues, programming, computer administration, design and so on. The site also includes comics, novels, philosophy essays, and magazines. Most of the texts are in English or Spanish and can be downloaded as high quality PDFs.
All the books can be downloaded and used without charge, but check the license of each title carefully before redistributing, since in some cases some restrictions may apply.