Although this isn't a new idea, it's the most interactively satisfying version I've ever seen, and the fact that it was created by a 14-year-old with the help of his twin brother makes it that much awesomer. It's a basic "powers of ten" visualization starting at human scale from which you can scrub downward smaller than quarks or upward to the scale of the entire universe. All the items in it are clickable for more information. But for reasons I can't quite put my finger on, my favorite aspect of it is the little twinkling animations it includes, from sunlight reflecting off the water below the Hoover Dam to Bohr-ish electrons circling a Mickey Mouse water molecule. Also, it's funny that Dysnomia (Eris' moon) and West Virginia are comparably sized. I don't know why I find that funny; I just do. I've embedded it here but to truly appreciate it you ought to go to Cary and Michael Huang's website and see it full-size. (It is a Flash animation which means it will not work on your iOS devices, sadly.)
This item via my college classmate Kathy Surpless on Facebook.