If you regularly have to resize images then JustResizeIt! provides a simple and convenient instant resizer with drag-and-drop support.
JustResizeIt! allows you to transform images into preset sizes of your choosing by dropping images into the corresponding box. The default sizes are 50%, 800 x 800 pixels and 1280 x 1280 pixels. You can create new image size presets by clicking on the 'Settings' tab. When you're ready, you can simply drag images into the box of your choice.
A progress bar keeps you informed of progress. When finished, JustResizeIt! displays thumbnails of your images which you can drag to the desktop or an application window. You can also change the size of the images afterwards if you want. You can create a different image background for each preset box so that you can recognize each by color and figure out which box represents which resizing dimensions, although they're all labeled so you should have no problems.
JustResizeIt! is a colorful and interesting way to resize images. Its flexibility and the fact that it's based on the glossy Adobe Air interface means it looks pretty slick too.