ImageOptim - Faster web pages and apps.
FILEminimizer Pictures - FILEminimizer Pictures compresses JPEG photos, TIFF, BMP and PNG images and pictures by up to 98%.
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
Shrink O'Matic - Shrink O'Matic is an AIR application to easily (batch) resize (shrink) images.
Compressor.io - Optimize and compress your images online. Compressor is a lossy and lossless photo compression tool.
Pinga - Think it, get it. Get Anything Delivered.