Squash 2 for Mac - The easiest way to compress and optimize images for the web
PhotoPenguin App - PhotoPenguin is a completely free batch photo editor with support for cropping, resizing, adding watermarks, and converting photos to other formats. It works on the user's device, using the capabilities of modern browsers.
punchi.me - Edit one or several images in a few clics.
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
Image Resizer for Windows - Lets you resize images by right-clicking.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.