Adobe Reader - Adobe Acrobat Reader is the most reliable, free global standard document management system available.

Bookworn – Online eBook reader which also allows you to create your own uploadable library of ePub books.

Calibre – Freeware, open source ePub reader and library manager for Linux, Windows and MAC. It has many features including eBook format conversion, search eBooks, etc.

Create your e-bookstore – No investment. Pay as you sell. Sell your ebooks on any device.

ePubReader –  A free plugin for Firefox which enables you to read ePub books. For Linux, Windows and MAC.

FBReader – Freeware ePub reader for Linux, Windows, MAC, Maemo, FreeBSD, Android and a number of other platforms.

Foxit Reader  – Free PDF reader for Windows.

Ebook Library Software – Easy and powerful program for E-Book library management.

Lucidor – Freeware ePub reader for Linux, Windows and MAC.

TreePad Viewer – Free ePub reader for Windows (a Linux and MAC version is on the way as well). uRead has a Chinese and an English version.

Free Ebooks For Your iPod, PDA, Smartphone, Blackberry etc. 

www.gutenberg.org

www.manybooks.net (Make Use of Review)

www.feedbooks.com (Make Use of Review)

www.booksinmyphone.com (Make Use of Review)