Keith Stuart recently posted a wide range of answers to the question of where good game ideas come from. Excerpt:
Art has proved a fecund source of game ideas. Tetsuya Mizuguchi was inspired by Russian artist Wassily Kandinsky to create Rez; Ken Levine drew on the Art Deco movement for Bioshock; Uncharted co-lead designer Richard Lemarchand looked at the works of Victorian painters such as David Roberts and Caspar David Friedrich for the exotic locations that Nathan Drake discovers. And countless dungeon designers have looked at the complex works of MC Escher and Giovanni Battista Piranesi for their labyrinthine environments.
— Keith Stuart @ The Guardian