Here's a delightful little toy: The Scale of the Universe is an interactive graphic that lets you scroll from the very largest to the very smallest sizes possible, with representative examples at each size. (Note: it has background music, but you can turn that off. Also, it is Flash-based, so may not work in all browsers.)
I've seen versions of this done as film, but there's something just plain fun about being able to scroll in and out to compare sizes. Well worth checking out, and a nice little educational tool...
