End your dependency on gasoline with the Honda FCX Clarity ($600/month; Summer 2008). This next-generation fuel cell vehicle runs on hydrogen, which allows it to emit only water instead of nasty fumes. It has a driving range of up to 280 miles, and offers the equivalent of 74 mpg thanks to the entirely-new Honda V Flow fuel cell platform on which its based. Unfortunately, hydrogen stations aren't exactly commonplace, which is why sales of the vehicle are limited to SoCal for now. Still, if you're looking to do your part for the environment, it's about as green as you can get.