Nap room. Seriously. I'm often dragging a bit by 3-4PM, between general tiredness and food coma from lunch. I'd love to be able to crash out for an hour or two, and come back to what I'm doing refreshed.
When you bike or take public transportation to work, you can't sneak a nap on your lunch break in your car. A nap room would be oh so helpful, and would dramatically aid productivity for sleepy employees benefiting from a power nap.