Laurence Kim has a great post on retouching photos entitled Tutorial: How I Retouch.
Laurence walks you through his whole process for retouching photos, specifically head shots.
Here's Laurence's before image, before any retouching.
And here's the result after Laurence has worked his magic and done his photo retouching.
As you can see, Laurence does an amazing job at retouching photos.
Check out the full article here.