Kevin Kelly: Better Than Free, a nifty essay on salable value in copyable products. What isn't clear for the affected pre-digital industries (e.g. music) is if a new model based on these values can bring in as much revenue as the old model that depended on scarcity.

A commenter on Kelly's site links to The Work of Art in the Age of Mechanical Reproduction, by Walter Benjamin, 1936. Wikipedia article.