Google Maps (Japan) + "Real-time" Radioactivity Readings
radioactivity.suminb.comI wish this chart did a little more to explain the meaning of the units. A big red dot corresponding to 559 nano-greys / hour (the highest reading when I viewed the chart) probably doesn't mean anything to most people.
That rate is about 2.33 x the world average background radiation level (ignoring quality factors and assuming 1 GY = 1 SV) and listing that alongside the raw units would be helpful.