The Antikythera Mechanism
an Astronomical clock from ~100 – 200 BC found in a shipwreck near the island of Antikythera.
Optical Lattice Atomic Clocks
Proposed in 2001 by University of Tokyo Professor Hidetoshi Katori, these are very much more accurate than standard atomic clocks. They are accurate enough to measure relativity and geologic density. Experimentally demonstrated in 2005.
Jun Ye, Boulder Colorado Strontium Optical Lattice Clock
10,000 Year Clock
Astronomical Skeleton Clock
Commissioned by Mark Franks in Chicago. Built by Buchanan in the UK.