After spotting Steve Wozniak's bad-ass "I could cut steak with this thing" metal business card on Cult of Mac, I believe I managed to track down the company that makes them. Judging by the background of their sample photos, it seems the card came from U.K.-based PlasmaDesign, which produces and sells stainless steel business cards in the U.S. and the U.K.
The cards are created through a combination of photochemical etching and good ol' cutting (we assume stamping), depending on the design, and if regular stainless steel etched into two shades is too boring for you, PlasmaDesign can also tint the metal into seven different shades using a complicated process called electrophoresis, which I could not adequately explain to you if I had a gun to my head.
The salient selling points of a metal business card are that they stand out and that recipients are presumably less likely to throw them away, but I wonder two things: 1) What is the environmental impact, vs. paper cards, and 2) Do these things set off airport metal detectors?