Resizing.app - Image resizing has never been so simple with free online resizing.app. Convert, optimize, resize images with ease and for absolutely free.
Responsive Viewer - View multiple screen dimensions in one view
Image Resizer for Windows - Lets you resize images by right-clicking.
Responsinator - Designed to test responsive websites on different devices.
punchi.me - Edit one or several images in a few clics.
Multi Screen Test - Test your site at different screen resolutions & devices.