The Scale of the Universe 2
The Scale of the Universe 2 - http://www.htwins.net/scale2/
This a great way of gaining some perspective of the universe from the smallest (Planck length) to the largest! It represents how little and meaningless we really are (if you round). Here's a link to a previous blog about that.
It is also a great way of learning/reviewing unit prefixes in comparison to an actual object. Furthermore, it shows the entire electromagnetic spectrum! The wavelengths can be shown relative to objects of similar size.
The ease of use and a couple Easter eggs make this a great discussion piece for students and adults alike.
It reminds me a lot of the "Powers of Ten" video (below) which is a classic! I highly recommend it!
Enjoy!