In his book, Free Culture, Professor Lawrence Lessig describes the importance of "mixing" (of other's creative work) to creativity (in general) and explores the dampening effects of certain changes in the copyright laws, including extension rules, on works of culture.
In his weblogs, Lessig often points to samples of mixing, and most recently, he's pointing us to the winning mixes in the CC (Creative Commons) Mixter's "The Fine Art of Sampling Contests."