FILEminimizer Pictures - FILEminimizer Pictures compresses JPEG photos, TIFF, BMP and PNG images and pictures by up to 98%.
ImageOptim - Faster web pages and apps.
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
Compressor.io - Optimize and compress your images online. Compressor is a lossy and lossless photo compression tool.
Shrink O'Matic - Shrink O'Matic is an AIR application to easily (batch) resize (shrink) images.
Optimizilla - Optimizilla is an online image optimizer uses a smart combination of best optimization and lossy compression algorithms in order to shrink JPEG and PNG pictures to the minimum possible size while keeping the required level of quality.