The topic of composition came up during the last challenge and recently I saw that Susan Sorger of 'Entourage Art' had posted some links (3,4 and 5 below) at CGA, so I figured it would be a good topic to post some links on and start discussions on.
Composition and Design Principles
NatureScapes.Net - Guidelines for Advanced Composition and Image Design, by Arthur Morris
THE ART OF COMPOSITION - Landscape
Photography Composition Articles: Landscape Composition Rules.
Art Composition and Perspective in Paintings
Of course these relate to traditional art of photography, but the rules are applicable to any visual media.