Single-Axis devices are by far the simplest. Put an electromagnet at the bottom of an elevator shaft, turn it on, and see what happens as you turn the power up.
Harnessing the Earth's magnetic field is alot more difficult, but still doable. How do you think flying saucers fly? (yes, they do exist, but no, they're not alien...they were designed and built by sectret angencies of our Government...or at least that's what I believe)
I still dont see why people dont think of practical ideas that would work...like a self-powered generator!