Local cooling is a free application you can download to help you save energy: it cuts your PC's power consumption by using a more effective power save mode.
While I'm sceptical about the idea of using this instead of turning your PC off whenever you can, it could certainly be useful to install on company computers, and I like their league tables of top energy savers, harnessing competitive urges to save the planet.
Related: Green tips for computer energy savings | Donate your spare computer (cycles) to climate change
From: BEST OF 2008: Eco-friendy and sustainable shoes