calibre - Ebook manager, viewer & converter
FBReader - FBReader is an e-book reader for various platforms. Features:
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Haihaisoft PDF Reader - Haihaisoft PDF Reader is the name of a free to use PDF reader and printer that is extremely simple to launch.
Cool Reader - Fast and small cross-platform eBook reader for desktops and handheld devices