Speaker panels can be a bit overwhelming, because there end up being so many people on stage, which makes them a special problem. We did an interesting thing for the speaker panel at 360iDev which I think is worth talking about.
Any question was supposed to be taken by only one panelist, and then there was a separate section of three people (including me!) for strong opinions. One of us was supposed to weigh in after, only if we disagreed.
I thought this was an interesting strategy because it limited the number of people speaking (a problem on larger panels) and also eliminated the dull “I agree and here’s why I agree” answer. I’m not really into arguing for the sake of arguing but it was kinda fun to be expected to disagree!
I’m moderating my first panel soon so I’m thinking about how you make things more engaging and encourage differences of opinion. This wasn’t a perfect solution (pretty sure there isn’t one) but I think there was a lot more dissent than I usually see, and that made it one of the more entertaining panels I’ve been on.