IrfanView www.irfanview.com (Windows)
IrfanView previews images (or even audio and video) and then converts or optimizes them without opening a separate editor.
Paint.NET www.getpaint.net (Windows)
This program is probably the closest thing to Photoshop you can get free, courtesy of a student project.
Picasa www.picasa.com (Windows | Linux)
Google’s photo manager makes it easy to get pictures off a digital camera, organize them, and even edit and share them.
Picnik www.picnik.com (Web | Flash)
Instantly edit pictures in this Web site. Upload images from your computer, Flickr, Picasa, or elsewhere.
Another online pic editor, pikifx .com emphasizes special effects such as added text and borders.
rsizr.com (Web | Flash)
With one of the best Web interfaces yet—all in Flash—rsizr.com incorporates smart resizing to avoid distortion.
Splashup www.splashup.com (Web | Flash)
Another beauty with a Flash interface, Splashup sets itself apart with multi-image editing and a full-screen mode.
Windows Live Photo Gallery HTTP://get.live.com/photogallery (Windows)
Windows Live Photo Gallery gives Picasa (above) a run for its money, with many of the same photo-enhancing and sharing features—red-eye reduction, exposure adjustment, cropping, color, sharpen, and auto-adjust. What’s more, Microsoft serves up histogram adjustment, panorama creation, and photo-CD burning.