I can't say I'm quite as juiced about knowing that it's possible to buy a slice of copper electrical cable that once hung over the Hoover Dam gorge, but seeing Mack Reed of Heavy Little Objects get so excited about it has rubbed off on me:
This is almost the holy grail of heavy little objects: a thing with history, patina, functionality, exciting manufacture and moving parts. Jesus, it made me one happy tool-using ape to find this: a chunk of the original copper electrical transmission line installed during construction of the mighty Hoover Dam.
I can't actually find where you can buy a segment for yourself. There doesn't appear to be a listing on the Bureau of Reclamation's Hoover Dam page. Maybe you have to go to Nevada and buy it on site?