As a creative tool brainstorms have taken a beating the past couple years. The key is setting expectations and organization. Don't throw a bunch of people into a room and expect magic to happen. Some tips...
1. Define the goals. Let the team know what the problem is that they're solving and describe criteria.
2. Appoint a leader. Keeps conversation moving along and polices judgement. Flags tangents.
3. Appoint a scribe. Documents all of the ideas on a flip chart or white board. Ideally in full view of the group.
4. Don't be critical. Nothing kills the desire to get involved like judgement. You can debate and argue later.
5. Embrace the wild ideas. The crazy thoughts can always be scaled back.
6. Set goals. More ideas are better so go for volume. Set motivating goals like, "Let's come up with 25 new ideas."