For me, the latest invention affordable to the common man is the new LiFePO4 type battery.
You get more cranking Amps, the capacity to crank even when they are discharged of most of its nominal capacity, the ability to re-charge at lightning speed and incredible weight gains over lead/acid technology.
People spend thousands in Carbon Fiber to reduce weight in racing vehicles but many are still carrying a big chunk of lead around. There are a few threads going on here in Advrider about these batteries but they are still unknown to many.
A few links: