TinyJPG - Compress JPEG images with perfect quality and file size
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
Promo Instant Image Resizer - Automatically optimize images for web & social media (free!)
DVDVideoSoft Image Convert and Resize - Free Image Convert and Resize is a compact yet powerful program for batch mode image processing.
Compressor - Compressor adds power and flexibility to Final Cut Pro X export.
Ralpha Image Resizer - High-speed image batch conversion tool