Happy Earth Day, everybody. We hope you've been out riding a bike, planting a tree, or recycling to celebrate the one day of the year dedicated to being green. Zero-emission vehicles have been a topic of discussion in the automotive world for years, but only recently have many of the concepts picked up steam and actually been released. Others, however, haven't been so lucky, finding it difficult to find funding for the rocky frontier. Check out the Chevy Volt, the Tesla Roadster and more in our list of 10 Cool Electric Cars.