This one just blows my mind. The defined and reproducible patterns are just amazing. Each frequency is unique. Couple that with the fact that everything in the universe is vibrating. And each frequency of vibration brings its own individual pattern.
Click the link at the bottom for a much longer version of the video.
What you're watching is the Chladni plate experiment, as performed by YouTube science-and-illusion wizard Brusspup (he can also coax water into a zig-zagging stream, and make Rubik's Cubes that aren't Rubik's Cubes).
When physicist Ernst Chladni performed this experiment in the 18th century, he did it with flour instead of sand, and made his metal plate vibrate with a violin bow instead of a tone generator, but the end result is the same: when the plate vibrates at a steady frequency, the particles on its surface arrange into a beautiful pattern.
The particles (sand, in this case) are arranging themselves along what are called "nodal lines" – narrow curves of motionless calm that criss-cross the otherwise vibrating surface. As the frequency changes, so does the distribution of these nodal lines, which becomes increasingly intricate at higher frequencies.