NASA's Got the Time
If the old cesium and rubidium clocks were not accurate enough for you, contact NASA's Jet Propulsion Laboratory. Their newest design is a low-friction model. It seems previous containers of the ionized atoms used to gauge the passage of time would rob energy from the atomic system, thereby introducing errors. The new device uses an ion trapping field, which holds a wad of ionized mercury atoms in a near frictionless volume for a more perfect count. You can set your watch by this one; it is accurate to within one minute every 10 billion years.