IrfanView - IrfanView ... one of the most popular viewers worldwide.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.