This is a video of Matt Giles tiling his kitchen floor with 27,000 (although I only counted 26,672) British pennies. That's £270 worth, or cheaper than you it would probably cost to buy actual tile or hardwood. Plus if you fall on hard times you can always take a sledgehammer to the floor and realize just how impossible it is to separate pennies from epoxy.
Keep going for the video but if you're interested in doing something similar Matt posted a complete tutorial HERE.
Thanks again to Luc, who plans on tiling his floor with real gold doubloons because he's a rich pirate.