http://www.gameshot.org/?id=6687 This is a very nicely done flash thinger that represents the scale of a great many things, from quantum foam to the visible universe, relative to each other. Like, you can actually see that the Burj Khalifa, the tallest building in the world, rested on its side is longer than the Vatican City. It's set to very soothing music. Click on any of the objects for a few facts about it, its size. Scale back and forth by dragging the scroll bar at the bottom, or using the arrow keys.
More than just finding it interesting to get a better idea of distances, I found it strangely moving to just very slowly scroll along and see each unit shrink or grow out of sight. Some people say that things like this make them feel insignificant. I don't have that feeling though. It's in our nature to want to be cared about, and nobody should get rid of that. However, when you can let go of it for a few minutes, be content for a moment to just exist, and simply contemplate the universe with the aid of something like this, there's a sense of awe. It's beautiful.