calibre - Ebook manager, viewer & converter
DealOz.com - Save time. Save money. Discover. Search new and used books, textbooks, and ebooks using the most trusted shopping comparison site, DealOz.com.
FBReader - FBReader is an e-book reader for various platforms. Features:
AbeBooks - AbeBooks has millions of new & used books, rare books and out of print books.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices