Mark / Mike,
I enjoyed your podcasts on brainstorming! While many suggestions were right in line with what I learned and started practicing about seven years ago after reading a book entitled "Rousing Creativity: Think New Now" by Floyd Hurt, you added several more helpful ones to the list.
What wasn't covered was how to get the participants to think outside the box - and that's where this book really helps. I especially like to use the lists, such as the "Verb Command Prompt List" that lists 140 verb commands such as "make it shine" or "give it texture" or "make it satirical." The idea is that you challenge the team to use the command to make them start thinking of solutions to the problem. I have one of the team members randomly draw from numbered pieces of paper between 1 and 140 so that we can't necessarily pick the easy prompts. It's amazing how many and how varied the ideas you can get from something like this. I've used the same list to solve tough engineering problems, to come up with marketing ideas, and to develop ideas to grow a church.
There are several other lists in the book that are interesting to use too. You mentioned that 15 minutes was about as long as you like to go with a session. I agree - However, using these lists, I have each group of 5 people (if there are more than 5 in the meeting) grab a number and work on solutions given the "phrase" they are given. I usually give them 10 minutes or so to brainstorm and then take another 10 to have them report to everyone in the meeting via flipcharts that get taped to the walls. We repeat this process several times - sometimes using different types of lists. During the process, they are also free to add ideas that combine other ideas or that don't use the phrase to get them there. In the end, we end up with lots of ideas. I found that without the lists, we end up with fairly stale ideas and things kind of go dead pretty quickly.
I definitely recommend the book to add to all of the good advice you gave in the podcasts.