It's all well and good to get the people in a room and stop them from shooting each other down in flames for a short while, but if they don't have (or don't know they have) the mental tools to construct ideas, in my experience not much is going to happen. The most exciting technique I've stumbled across is Charles "Hipbone" Cameron's Glass Bead Game, reverse-engineered from a game played by characters in Hermann Hesse's novel.The pieces, played on any node of the board, are ideas. Whenever there's a link between the node you want to play and another node that has previously been played, you must also come up with a way to link the ideas. That turns out to be an excellent basis for coming up with new ideas: all you have to do is forge a connection between two concepts. That connection happens in two places: on the board, and in the brains of the participants. This is no mere "put ideas up on a whiteboard" scenario: you're giving people the opportunity to change the way they think.
Mind mapping exercises discover ideas you've temporarily forgotten by following the connections between them. Glass Bead games create new ideas by creating the connections between existing ideas.
Brainstorming and the Glass Bead Game
Garth Kidd, Deadly Bloody Serious
http://www.deadlybloodyserious.com/2002/02/10.html