There are some excellent photo/image editing programs that are fully worth purchasing, however, there are a multitude of excellent free programs that offer more than what most of us actually need. So, if you want a program to edit your photos and don't have the sometimes hundreds of dollars to spare you may want to try one or more of these. Jim
The GIMP (Graphic Image Manipulation Program) This is an open-source project (freely distributed applications developed by different programmers whose common goal is to create excellent software). This challenges even the best photography software available. I'm still getting used to it (the GUI, Graphic User Interface) is different than what I'm familiar with, but little by little I'm appreciating some of the set up more. If you're even semi-serious about image editing I would HIGHLY recommend this software! Did I mention that it's available for free download? :) The link I have above takes you directly to the download page for the Windows version of the program. If you have a different OS just click the appropriate menu link on that page.
PAINT.NET I just downloaded this open-source program and immediately found it easy to use. From the developers web site, "Paint.NET is image and photo manipulation software designed to be used on computers that run Windows 2000, XP, Vista, or Server 2003. It supports layers, unlimited undo, special effects, and a wide variety of useful and powerful tools." It requires the most recent .NET framework 2.0, so if you're not sure you have that installed make sure you choose the package that includes it. It is a large download (49.1 mb), but from what I have seen already it is well worth it.
PICASA Google's free photo organization and editing program. If I didn't already have Canon's program (that came with my camera) up and running I would most likely be using this. I've only opened it a couple times, and each time was so impressed by its set up that I almost switched. Who knows I may eventually do so.
IrfanView Graphic Viewer An excellent image viewer packaged with numerous editing features. One of the things I like about this program is that it allows me to batch rename any number of files to whatever I choose (comes in handy for categorizing and remembering those vacation images).