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.
Digital Editions – Free ePub reader from Adobe. Runs on Mac and Windows.
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.
Lucidor – Freeware ePub reader for Linux, Windows and MAC.
MobiPocket – Free ePub reader for Windows, Blackberry, Epoc, HPC, Palm, Windows Mobile, Nokia and more.
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.