Decorator crabs are really cool.

Bonus: Drive & Listen (drive around cities while listening to their local radio)

Above from Akiyoshi Kitaoka.

Ambiguous Cylinders by Kokichi Sugihara is amazing.

More neat ones here and here.

Micrograph by Linden Gledhill.

Ostagram demonstrates the remarkable beauty of converging visual styles, performed via algorithm. [via Metafilter]
A related, singular effect can be achieved with this image triangulator.

Dynamic, resizable pixel art by Marcus Blättermann.