Shrink O'Matic - Shrink O'Matic is an AIR application to easily (batch) resize (shrink) images.
Aseprite - Aseprite is an art program dedicated to the creation of pixel art.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
Pixel Studio - The Pixel Art Is Always Fun
ImageOptim - Faster web pages and apps.
Piskel - Piskel is a website where designers online create sprites or pixel art.