EPUB Reader

If you want to read epub file on your desktop then try these.

MobiPocket
MobiPocket Reader is not only an advanced ePub books reader but is also a great professional books organizer. You can import books in PDF, ePub, or Office formats and organize them quickly. Just double-click a book and start reading.
The formatting of MobiPocket has an option to zoom into the book, useful for those who want to read the tiny text on the book. Also there is an advanced search box given on the top-right side which can drastically help in saving time.

EPUB Reader Firefox Add-On (Windows/Linux/Mac)

EPUBReader is a handy add-on for Firefox that can directly open any ePub format quickly. It is indeed faster and quicker. This add-on opens the ePub file just like you can open PDF file in Firefox browser. Just hit the download link of any ePub book and select Open. If you have already downloaded the ePub book, then you can open it with Firefox.
The interface is customizable, which means you can change the background colors, etc to your own liking. The navigations buttons are given at the bottom along with the option to change the fonts.