calibre - Ebook manager, viewer & converter
NeeView - Display two images simultaneously
FBReader - FBReader is an e-book reader for various platforms. Features:
Soda PDF 3D Reader - Read any PDF document like a book using our patent pending 3D technology!
ACBF Viewer - Comic book reader.
ComiXed - ComiXed seeks to be the ultimate digital comic book management system.