XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
PixBuilder - Free Photo Editing Software for PC
IrfanView - IrfanView ... one of the most popular viewers worldwide.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.
Fotografix - In addition to being totally portable, Fotografix has a ridiculously small footprint.