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.
FastStone Photo Resizer - Convert and Rename images in batch mode Support JPEG, BMP, GIF, PNG, TIFF and JPEG2000
BIMP - With BIMP you can apply a set of manipulations to an entire group of images!
Phatch - Phatch = Photo & Batch!
Bulk Resize Photos - Resize large photos in bulk