ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
Darktable - darktable is an open source photography workflow application and raw developer.
Ralpha Image Resizer - High-speed image batch conversion tool
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
OnlineImageResize.com - Free online image resizer. Resize your image fast and easy. Image resizer online!