If you want "saving the planet" to be part of your job description, consider becoming an energy efficiency engineer. Unless you've been living in a cave, you probably know that saving energy is a good thing. Not only does it mean using fewer of our planet's precious natural resources (like coal and gas), but everyone, whether they're a small family or a mega-corporation, can usually save money by doing so. In this role, you might advise developers constructing a brand-new skyscraper on the most energy-saving air-conditioning system, design trendy new power sources like wind turbines and solar panels, or help a large company reduce their carbon footprint by inspecting their building and offering suggestions. This job is flexible because it gives you the chance to work either one-on-one with consumers or with large organizations, and because it's a rapidly growing field, you'll always have plenty of career prospects. Engineers, who must also be science and technology whizzes, typically specialize in one area: Think heating, lighting, clean air, or eco-friendly building design.