As a believer in free markets, one of my favorite prediction tools is Intrade. The idea of Intrade is that people are allowed to buy and trade shares in things like the likelihood that Al Gore will be the next president, who will win Best Supporting Actor at the Emmies, whether Russian troops will enter Tblisi, etc.
People can make or lose real money on these trades, so they're more likely to seriously consider before making a choice. Looking at the Presidential election, one of the surprising facts is that Hillary Clinton is still trading in the $3.50 range. Barack Obama has recently dropped from a high of $68 to $60, and he continues to drop this week despite the so-called "convention polling bump." However, John McCain continues to hold steady, just under $40, which isn't hopeful for him.
I haven't done a study to see how accurate Intrade is at making election predictions (or invasion predictions for that matter), but I enjoy watching the markets.