The Cup Cafe in Tucson's Hotel Congress did this with real pennies. I don't know what medium they used, but the pennies appear to float between the transparent surface and the concrete floor beneath.
http://www.flickr.com/photos/wetchman/361104985/
Can anyone figure out what a penny floor comes to per square foot (minus of course the mystery medium)?

As soon as I saw this, I was going to post a picture of the Congress's floor. But you beat me to it, DianneS!

I believe that the medium is an industrial strength resin. Duh, of course it is. But I've no idea what kind.

We put penny tile in our bathroom (a green color, not copper) and the tile alone cost under $13/sq ft. We did it ourselves, so the cost of additional materials was the only additional cost. It's beautiful!

Tip for low light shots:

GorillaPod timer

erm, there's supposed to be an AND in there. oops.

You can get decently un-blurred shots if you brace against something and squeeze the shutter VERY gently. But a gorillapod and timer would be best.

I used white penny tiles in my bathroom with dark grey grout. It was not that expensive and they look great.

Whoooaahhh! Scroll down the page slowly, starting with picture one of these tiles at the top of your screen, and see what happens. . . . .

for shake less photos
keep elbows in
open both eyes
brace against wall or pillar
take off auto use fast shutter speed
from my bro the "famous" photographer

I enjoy these tiles and thought the stainless steel version were also cool in real life.

Is it just me or is the foreground of the top photo highlighting a big screw-up in the laying of those tiles?