My best (no particular order): Wheel, computer, printing press, electricity, steam engine, camera (syempre pah! ), telephone, telegraph, penicillin, microscope, money, and the sewing machine.
My worst (no particular order): bilogical weapons, nuclear weapons, the necktie (what practical purpose does it have?), internal cumbustion engine (sorry, he he he), plastic, money and a few more that I forgot what they're called.