I bought this book on Merlin Mann's recommendation.

See:

http://www.43folders.com/2009/01/27/creativity-patterns

http://www.43folders.com/2009/01/13/twylas-box

http://www.43folders.com/2008/11/26/twyla-tharp-failing-well

http://www.43folders.com/2008/08/27/book-heuristics

The book is very good and well worth buying. I'd also recommend the War of Art by Pressman. Both of these books are great for cultivating creativity in a systematic way.