Yet another good tutorial from Deviant Art. This portrait was done by Harbek. She provides some great tips for creating a portrait in Photoshop and you can clearly see the main stages of the painting. Note the way detail is applied to the image, with the brush size gradually going from large to small allowing for a much more realistic look.
Click on the first image to enlarge and click next to browse through the whole tutorial. [You can also see a .gif walkthrough of this tutorial here]