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.
Squash 2 for Mac - The easiest way to compress and optimize images for the web
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
Tinuous - An image converter batch-processing multiple files. JPEG lossless transformations are implemented.
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.