After my post “Starting to Use Photoshop Brushes?†I was reminded of other features I have barely touched for years. Displacement Maps is another feature that I often forget and I know many others seldomly use. This tutorial gives a nice example of Displacement Maps in use: Use The Displace Filter & Displacement Maps To Make A Realistic flag.
This guide is written for use in Adobe Photoshop Elements, but should work just as well in the full version of Photoshop. The website PhotoshopSupport also seems like quite a good resource regarding Photoshop, but I have just briefly glanced though the site.