Amtrack is pretty proud of its 150 mph Acela Express. California will be pretty proud of its 220 mph high speed rail project, if it ever happens. Japan is poised to leave us all in the dust, though, with a new maglev train slated to connect Tokyo with Nagoya and Osaka at a knuckle-whitening 313 mph.
This maglev line has been under consideration in Japan for the last 40 years or so, but it just recently got final approval to begin construction in 2014. Most of the track has actually been built already, but there's whole heap of mountains that they're going to have to blast through, meaning that the first segment of track isn't going to open for business until sometime around 2027, by which time we'll probably be riding around in flying trains anyway.
The reason maglev trains can go so fast is that they don't have to waste their time with piddly nuisances like engines or wheels. Instead, they float above their tracks on a frictionless magnetic field. To move, a magnetic wave is sent down the track from one end, and the train surfs it all the way to the other, limited only by the energy it takes to overcome air resistance.
At the moment, there's only one single commercial maglev route in daily passenger operation. It's in China, running 19 miles from the Pudong International Airport into not quite downtown Shanghai. The trip takes all of seven minutes, and having taken the ride myself, I can tell you that it's an odd combination of incredibly awesome and slightly silly: it takes the train about three minutes to accelerate to its top speed of 268 mph, and then another three minutes to slow down again, leaving you with a mere thirty seconds of rather shaky full-speed cruising time.