Real time statistics for current population of any country. Real time data on population, births, deaths, net migration and population growth.
This site shows various demographic statistics for every country including some based on projections in demographic trends in the given country. If the current trends hold (which they won't, but that is still an interesting measure), the entire Japanese population will disappear in 1,000 years according to this Global Post article.
Via Seth Dixon, Steve Perkins, Rich Schultz