Idea futures markets should make it possible to quantify answers which people would otherwise be vague or imprecise about, and can potentially insure that the answers are unbiased forecasts from people whose past forecasts have been good.
The U.S. Idea Futures Exchange is a web-based service which allows people to invest play-money in issues relevant to U.S. financial, economic, and political controversies.
To get started, you should register here to create an account, find some claims in which you are interested (the Claims/Activity page provides a number of ways to find claims), and then go to the Trade page to place an order to buy or sell some contracts. You are encouraged to join the mailing list that is used to discuss the market.
A more theoretical introduction to idea futures, written by Robin Hanson, who pioneered the concept, is available here.
Here are some examples of similar exchanges: