Image Resizer for Windows - Lets you resize images by right-clicking.
Assetizr - A super fast image resizing tool
Resizing.app - Image resizing has never been so simple with free online resizing.app. Convert, optimize, resize images with ease and for absolutely free.
Squash 2 for Mac - The easiest way to compress and optimize images for the web
punchi.me - Edit one or several images in a few clics.
EasyBatchPhoto - EasyBatchPhoto is a utility that lets you batch-compress, resize, and convert your photos.