If you want to mess with your mind a little, load up this flash piece from Nikon that puts the size of things in the perspective of orders of magnitude. It takes a while to load. Also beware that it's set to a static screen size so make sure you can see the bottom where the order of magnitude that you can click on to navigate are visible. I think the part that messed with me the most is when it shows the size of a carbon nano tube which turns out to be smaller than DNA. The messages about boundaries in size are interesting, but they keep showing up which is a little annoying, but it's still amazing to try to think about the sizes.