I was looking at my iPod mirror when an idea came to my head. I dont know how practical this may seem... but here goes:
Suppose we were to take a closed cube. All the inner sides of the cube are mirrors. Inside the cube is not vacuum.
And we were to let some light into the box.
The light will reflect off the mirrors forever and the air inside the box will heat up, ultimately heating the box itself.
We could extract this energy and heat water or something that could drive a turbine and produce electricity. Maybe if this works out, it could solve the world's energy crisis once and forever.