As a web designer I spend quite some time in Photoshop, I've picked up some useful stuff on the way.

Name	Difficulty	Description
Polaroid		Create great looking Polaroid like images.
Unsharp Mask		Make resized image a bit sharper.
Black & White to Color		How to easily add color to black & white pictures.
Photomerge		Using the merge tool too easily merge panorama image.
Change Eye Color		Explains how to change the color of someone's eye.
Toolbox		Learning about the photoshop Toolbox