Adobe's Photoshop CS2 is the best program there is for editing digital photos or any image file. This one does everything you can imagine. It's not cheap, but you'll get your money's worth. Photoshop CS2 is the standard program for professional photo editors and desktop publishing professionals. The latest version lets you automate a lot of tasks -- downloading pix from your camera, resizing and renaming them, and it has endless tools for retouching, sharpening, cropping and filtering your photos. If you've bought a serious digital camera, or need to make a professional looking web site, Photoshop is the way to go.
Adobe lets you download a free trial for Photoshop from their site.