Squash 2 for Mac - The easiest way to compress and optimize images for the web
Resizing.app - Image resizing has never been so simple with free online resizing.app. Convert, optimize, resize images with ease and for absolutely free.
punchi.me - Edit one or several images in a few clics.
Caesium Image Compressor - Compress your pictures up to 90% without visible quality loss.
EasyImageSizer - EasyimageSizer, now named Lenna, is an online tool to batch compress, resize and rename images.
ImageResizer - Free online app to crop and resize images