I've got three cool reosurces related to the scale of things we've been talking about in our house lately.
I'm cheating with the first one because I already posted about it but it's Cells Alive!. On that site you start with a picture of a pin and steadily zoom in one a human hair, pollen, blood cell, etc. until you get to a rhino virus.
Over on Evolved Homeschooling there's the coolest post on a site where you can view a Blue Whale...life size. Sort of.
The one that I thought was neatest was the one we used yesterday at KidsGeo. The first page relating to the size of the earth shows it in relation to all the planets in the solar system that are smaller then it. The next shows it relation to the other planets, the next to the sun and so on. It goes on until the sun is the size of a pixel compared to Antares and Betelgeuse.