Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
jPDFViewer - Use jPDFViewer Java PDF SDK to integrate a PDF reader right into your Java application or website.
calibre - Ebook manager, viewer & converter
MuPDF - MuPDF is a lightweight PDF and XPS viewer.
Okular - Okular is a universal document viewer based developed by KDE.
Altarsoft PDF Reader - Altarsoft PDF Reader is a simple to use PDF files management program that allows its users to view PDF files, encrypt the files and even annotate these files as well.