Crooked Timber reports that the lead in the Iowa Electronic Markets' 2004 US Presidental Election Winner Takes All Market shifted to Kerry (blue) earlier this month. Unfortunately (as you can see in the image to your right), the lead has shifted back to Bush (yellow). Current asking prices are 0.501 to 0.499.
I blogged about the IEM back in June. In the same entry, I mentioned Tripias.com's State by State, which currently shows Kerry winning by a substantial margin. It is not as slick as the New York Times' flash-based 2004 Election Guide, but State by State allows you to use actual polling data to generate custom maps.