Everyone always talks about how great photoshop is, and this is sort of like that. An open source (free) program, called The GIMP is an excellent alternative - and it's got all the high quality features. I've been using it for the AnimeIowa Picture Gallery, and I'd like to upload an example. The original image was super dark due to the backlighting, but because of the dodge/burn tool with the Gimp, we can actually get a high quality photo from it!
BEFORE -------------------> AFTER