Creepy Door Photoshop Tutorial
This is the type of image they use to promote many different horror movies and similar other artists. I think that it is a good lesson but is really very niche specific.
This is another tutorial from the 9tutorials guys. Very easy to follow instructions and additional benefit of this Photoshop tutorial is that you will have a good understanding of shadowing and how to add curves to an object with out the object becoming distorted. While the application itself is very niche the skills learned from can be applied to a number of different photoshop projects.