ImageAlpha - ImageAlpha is a GUI for pngnq and pngquant.
ImageOptim - Faster web pages and apps.
SqueezeFile - squeeze your files to different dimension.
FILEminimizer Pictures - FILEminimizer Pictures compresses JPEG photos, TIFF, BMP and PNG images and pictures by up to 98%.
Shrink O'Matic - Shrink O'Matic is an AIR application to easily (batch) resize (shrink) images.
Optimage - Advanced image optimization tool