This list of Photoshop Tutorials has a lot to see. Some of it you will know, and some of it will make you rethink how you are currently doing things. This is a must bookmark page.
28 Incredible Photoshop Image Manipulation Techniques and Tutorials : Speckyboy Design Magazine:
"All of these tutorials will show you how to take the simplest image and create something eye-popping and professional. Each one uses different techniques to achieve the result, and I am sure you would agree they are all amazing."