There's so many options, perhaps you can narrow down the concept of prediction?
Are you looking for a prediction of choices people make (ie - chair predictions, confabulation-style)? Or, are you looking for a more traditional event style prediction (lottery numbers, major event, etc.)?
Rick Maue's Fate can play as a powerful prediction. It also allows for a good deal of audience participation, with 5 spectator's assisting through the demonstration. It's also incredibly under-priced, but that's pretty much Rick's MO.
Patrick Redford has a fantastic Chair Prediction (Ensconced Fundament), which, while a bit pricey, is worth taking a look at.
Or were you thinking more along the lines of a locked box on stage, with a prediction shown at the end? In that case, there's items like these:
http://www.hanklee.org//xcart/product.php?productid=2752&cat=7&page=5
Smaller in size, but certainly looks great. I believe Iain owns this, so you could speak with him about whether or not it suits your needs.
For a low-cost method, Jay Sankey's Omnilopes can work on stage.
There's also expensive versions. You could also check out Corinda, there's always something there to help you out!