I'm one of those who think that while global warming may be happening, given the evidence, I still doubt that we are to blame for the recent warming cycle. I've followed the concern for years now, read about everything I can get my hands on (even fiction on it, State of Fear, by Michael Crichton), and nothing compelling has convinced me that we are at fault and can really do anything about it. (When I first heard about it, I was. But most of the stuff since has convinced me it's a natural cycle.)
I had it on my list anyway, but at a friend's urging when I told him the above, I made sure I saw Al Gore's An Inconvenient Truth.
Well, I'm still not convinced we are at fault, but I am now convinced there's no reason not to take steps to reduce emissions wherever possible. Gore does a great job of making a case that there won't be significant economic impact if we do take such steps.
And, if you haven't seen it, it's worth a few minutes of your time. It's a good show. Make sure to catch the updates in the extras.