Planning Poker turns the Wideband Delphi estimating technique into a card game. I’ve used Delphi on past projects to flush out assumptions and to get rough-cut estimates, but it was never as much fun. Mike has an on-line version of the game at planningpoker.com. And, in true web 2.0 style, it’s a Rails app.
If the chance to hear Mike speak comes within reach, grab it. He’s full of the engaging, friendly wit that you need to arm yourself with for discussions with upper management about planning and tracking, and his presentations have awesome footnotes.