The most overlooked aspect of digital image editing is monitor calibration -- the process of making sure that your monitor accurately represents your images, and hence accurately represents what you are doing to your images when you tamper with them. This is something that almost all the pros do but that most amateurs have never even heard of. It is one of the things separates the "big boys" from the people who are "just getting into photography".
Uncalibrated monitors are lying bastards. An uncalibrated monitor might represent an image as being, say, less contrasty than it really is, or as having a color cast that it doesn't really have. Thus if you try to correct these problems by using some photo editing software, you might be making the real problems worse, or creating different or more serious problems. Color correction requires trusting your eye, but you can't trust your eye unless you can trust your monitor. Thus any money that you spend on digital image editing products for the purpose of color correction might as well be pissed down the drain if you don't calibrate your monitor. That's at best -- for often your images will look better untouched than if you modify them by reference to an uncalibrated monitor.
The solution requires getting a calibrator. The first step is to decide which one to buy.
Step 1: Choosing a Calibrator
Currently the most popular brands of monitor calibration devices are X-Rite and Datacolor .
As a rule, X-Rite products are slightly more expensive and tend to be slightly better. But I use a Datacolor product. The Datacolor Sypder3 was already out when I bought a used version of the Datacolor Spyder2 for $50 on ebay. It works very well.
Step 2: Using a Calibrator
Using a calibrator is easy. All you have to do is plug it into a USB port, hang it in front of your monitor, and run the accompanying software.
You don't need to know how it works. But if you're curious, how it works is ingenious. By running through a series of shades of red, blue, green, and gray, the computer learns about the precise ways in which the monitor misrepresents the color data, and from this it figures out a way to outsmart the monitor in the future. In the future, it will lie to the monitor in such a way that the monitor's own lies will end up displaying the desired colors, so that the lies will all be canceled out in perfect fashion.
Step 3: Buy, Use, and Re-sell?
One option is to buy a calibrator on ebay, use it, and then turn around and re-sell it. This is roughly the $15 solution, assuming one will end up losing about $15 on shipping and ebay fees.
This solution is much better than not calibrating at all. However, professionals probably wouldn't do this, as a monitor's chemistry changes slightly over time, so that if one is being really picky then it is important to recalibrate on a regular basis: say, once a month.