TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
ImageOptim - Faster web pages and apps.
OptiMole - Optimole makes your images weigh even 80% less while looking just as good!
FILEminimizer Pictures - FILEminimizer Pictures compresses JPEG photos, TIFF, BMP and PNG images and pictures by up to 98%.
TinyJPG - Compress JPEG images with perfect quality and file size
Shrink O'Matic - Shrink O'Matic is an AIR application to easily (batch) resize (shrink) images.