WTC debris
I only did a cursory search on this, since it dropped me into about four million Evil Conspiracy sites, but most the WTC debris was shipped out for normal steel recycling in Asia. Almost anything with steel that you buy that was made in China might have a bit of that metal in it.
I hadn't heard about the Rovers. That's cool. I wouldn't have minded seeing debris from the lost Shuttles formally recycled into new space probes either.