Solar panels, wind turbines and biofuels get all the green attention. But sometimes the best ideas are the simple ones. Verdiem has one of those ideas. The Seattle-based start-up sells software that manages energy used by computers. That's no small amount — the Department of Energy estimates that computers and computer monitors are responsible for 13% of the electricity sucked up by commercial enterprises, and much of that energy is wasted when PCs are left idling. Verdiem's software allows centralized power control over office PC networks, which means no more leaving your computer on all night. The savings are substantial — Verdiem estimates that since it began it has helped reduce electricity consumption by over 500 million kilowatt hours, and cut carbon emissions by nearly 500,000 tons. "This is moving from grassroots, environmentally conscious people to mainstream business," says Kevin Klustner, Verdiem's CEO. "Green IT is big."