Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
WinDjView - WinDjView is a fast, compact and powerful DjVu viewer for Windows with tabbed interface, continuous...
DjVuLibre - DjVuLibre: Open Source DjVu library and viewer
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
MuPDF - MuPDF is a lightweight PDF and XPS viewer.
EBookDroid - EBookDroid is an open source (GPL'ed) document viewer for Android based on the VuDroid code...