When discussing ideas the use of De Bono's 6 hats is a really useful tool - if anyone wants more info let me know - but for those who use it - have you tried this ?
Get an idea and then give 6 people a different colour to be but then every 10 mins change their colour. It encourages people to think differently.
People often see design or creative sessions as a nice to do...wrong. This came home to me when I read this quote by Brian Collins of Ogilvy & Mather
"Design is not a plan for decoration. Design is a plan for action" Keep that thought at the front of your mind when brainstorming.