Two things I always geek out over is Lego and Electronics. I love building things with both, and while I've seen some cool electronics Lego (Legtronics?) hacks this one is probably the most functional. Putting a resistor in the minifigs hands connects the resistor to a custom circuit that sends the resistance to a PC via a USB connection. There is also a way to test AA and AAA batteries.
David, the creative mind behind Robot Room, gives a ton of details about the build. Including wiring up minifigs and adding LEDs to their heads. The build is detailed at David's Robot Room page.
Found via Hackaday
