Stanza Desktop is a free program that will let you read or convert ePub documents; it will also assist you in transferring your books to Stanza iPhone/iPod Touch.
Stanza Desktop currently supports reading books in a variety of unprotected formats (including HTML, plain text, Mobipocket). Books in protected formats (such as Kindle books, books protected with Adobe DRM, and protected Mobipocket books) cannot currently be read using Stanza Desktop.
Stanza Desktop does not currently contain any library management features, or the ability to download books directly from the internet. For library management and conversion-related features, you may be interested in looking at the free Calibre project.
You can paste text to create a new e-book, or import e-books from a comprehensive list of file types, including Adobe’s EPUB, Amazon Kindle’s AZW, eReader’s PDB, FictionBook’s FB2, and Open ebook’s EPUB (Stanza’s native format). But the desktop version goes beyond this by letting you use non-e-book formats, such as PDF, TXT, DOC, and HTML, so you can turn just about any file with text into an e-book.
I must say that (on Windows 7) Stanza was not able to display epub documents, but only as garbage.