I've always wanted to see an electrical engineer debunk a 'free energy' device based on some kind of special electrical wizardry. I was browsing the EEVblog youtube channel (which has a lot of fascinating material, and the guy is clearly an expert) and I found this video.
The free energy circuit is debunked first in theory on the whiteboard, and then in practice after he builds the circuit. I'm sure he could debunk a whole lot of others too if given the time (and patience). It might be a bit hard to follow if you don't have a rudimentary understanding of electronics, but most people who have dabbled in this area at one time or another should get the gist of it.