Over in my alumni group, we're working on photographing anything against a white background. These are some images I made using (first) a wheat stalk and (second) a couple of pine cones. I like the clean, spare, Zen-like feel to this effect, don't you?
One way to do this would be to place the subject directly upon a piece of white paper, but in this case I stuck the wheat stalk and the pine cone branch into a jar and set the jar in front of a white backdrop. Light came from both left and right, and I reflected a bit of gold onto the wheat to give it some oomph.
Shooting straight down onto something poses other problems, such as how to light the subject so that you don't have harsh shadows and so that you don't block any light you may have coming down from above. Stay tuned!