Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
noesis - Rich Whitehouse's project web site.
XnConvert - XnConvert is an easy image converter for graphic files, photos and images available on Windows...
GraphicConverter - Graphic Converter for Mac and Windows, can converts image formats BMP, JPG, GIF, ICO, PNG, TIF...
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.