Philips Expanium EXP401: Smaller than reguar MP3/CD players, it plays 3 hours of music stored on cheap 3-inch CDs. What it doesn't do: Like any CD player, it's prone to skipping if you take it out for a jog. Price: $199
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.