At leapsecond.com, what started out as a hobby building digital clocks, has turned into a quest for the best time money (and time) can buy (short of what you can get when the taxpayers are footing the bill). As he says,
This simple goal resulted in a most interesting journey into electronics, horology, astronomy, test equipment, quartz oscillators, rubidium and cesium atomic clocks, hydrogen masers, frequency counters and phase comparators, GPS, Loran C, GOES, and WWV / WWVB radio receivers.
Definately some pretty strange stuff.
Of course, my favorite time site is nist.time.gov where you can click on your state and get the time to within 0.1 seconds (depending on your ISP jitter), and if that wasn't enough, you can go check out the NIST Physics Laboratory where they maintain a number of Cesium clocks, including the new NIST-F1 Fountain Atomic Clock (with accuracy to 2 x 10-15 seconds).
There's a problem with using cesium though, because the atoms are moving and measuring atoms that are moving is naturally an imprecise endeavor, research continues on the Trapped Ion Frequency Standard (I'd explain more, but I'm a bit behind on my Penning traps and non-neutral plasma reading).