Audible - Audible is the world’s largest provider of premium audiobooks and spoken word content.
calibre - Ebook manager, viewer & converter
LibriVox - free public domain audiobooks
FBReader - FBReader is an e-book reader for various platforms. Features:
Mobilism.org - A home for book lovers, app enthusiasts, and much more.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.