calibre - Ebook manager, viewer & converter
eBooks.com - eBooks.com is a leading retailer of ebooks, with a vast range of ebooks from academic, popular and professional publishers.
FBReader - FBReader is an e-book reader for various platforms. Features:
Kobo Books - Kobo Books is a best in the class eBooks and eReadering apps for many reasons.
Google Play Books - Google Play Books lets you search, preview, and buy millions of books using Google Book Search.
Amazon Kindle Store - The Amazon Kindle eBook store is the biggest and most widely used eBook store on the web.