TPS Clevelander Rob Holub sends along this link, asking conservative anti-global warming folk to put their money where their mouth is. The way I see it is as follows: Anti-global warming supports like to bring up sporadic examples of unexpectedly cool weather and then put forth the conclusion that all of this global warming nonsense is hogwash. The author of the blog post linked above says that those folks are remembering what they want to remember-- thus the bet. If you look at the whole picture, things may not support your position.
For what it's worth, I don't think the question is as much about whether the Earth's temperature is rising as much as whether it's humans that are causing that rise, or any further warming on top of the nature cycle of the Earth. As such, the bet shouldn't be a comparison of current temperatures to historical levels, but a comparison to a trendline estimate of where the Earth is naturally heading anyway. I guess it's not too surprising that no one has taken the bet.
It brings up the larger question: Should one be willing to put up money to lend credence to their positions? MR dealt with the issue a little while back, though I don't know how long ago and can't find the link. I could be convinced either way, though I suppose a staunch conviction in your theory could be offset by an even more staunch adherence to risk aversion.