Another link: Color theory in photos. Even though I use Photoshop a lot (and have done some okay things with it, in my opinion) there is always more stuff that can be done with it. Color curves! I shall have to attempt editing some of my photos in this manner at some point. . . but I have far to many to make it a consistent practice. :P
Another post on the awesomeness of messing with color curves in Photoshop.