Supposedly, the betting site BetUS.com has a list of global warming wagers they're willing to make (I couldn't find them on the website, could they be removed already?).
Like Gavin Schmidt in this article, I'm not too impressed. The bets are either poorly defined or so outlandish that they don't test the difference between the consensus position and the denialists. I think it's more of a publicity stunt than a real attempt to create a betting market, which is too bad.
I don't know who would take these bets, but whoever would take them should consider the even better odds that I offer - I'll give 1:20 odds that temperatures will drop in ten years, or 2:1 odds that temperatures will rise.
And meanwhile, I may have some good news on betting soon. We'll see...