ImageOptim - Faster web pages and apps.
Squash 2 for Mac - The easiest way to compress and optimize images for the web
FILEminimizer Pictures - FILEminimizer Pictures compresses JPEG photos, TIFF, BMP and PNG images and pictures by up to 98%.
Image Resizer for Windows - Lets you resize images by right-clicking.
Shrink O'Matic - Shrink O'Matic is an AIR application to easily (batch) resize (shrink) images.
punchi.me - Edit one or several images in a few clics.