Predicting the future is a quite difficult job, but this article helps. While the DARPA futures market has been doomed the NYT has invested in some research.
The Foresight Exchange and the Iowa Electronic Markets do the same thing but obviously lack liquidity and the chance to bet real money.
Tradesports one of the abundant online online betting exchanges allows a nicer bet with real money on some political topics as well. It has a longer history as an online sports betting exchange. It usually features sports betting, but nowadays also who will be Germany's next chancellor or the fate of Tony Blair in office.