Smashing magazine has an great collection of Photoshop tutorials. Anything from rendering products, lightning effects, retouching photos and improving their look, reflections, creating product boxes… you name it and it is probably there.

The list of tutorials is over 30 pages long, and that is not counting how long each tutorial is. So if you have a lot of free time to master your Photoshop skills this is a very good place to start; also a great page to bookmark since you won’t be done with those tutorials in a while and you might need them later.