Quick Resizer is the fastest and simplest app for resizing your images.
You can resize one or more images by dragging them on the app or opening them from within the app. PNG and JPEG files are supported, and the resized images will be optimized for use on the Web.
Simply drag your image file (or files--batch resizing is simple!) on the app, set the size and constraint for the resizing, and hit Return!
You can also set the app to quit automatically after processing images, you can change the JPEG compression quality, and the app will save your settings from launch to launch.