DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
Ralpha Image Resizer - High-speed image batch conversion tool
Darktable - darktable is an open source photography workflow application and raw developer.
FastStone Photo Resizer - Convert and Rename images in batch mode Support JPEG, BMP, GIF, PNG, TIFF and JPEG2000
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.