Which earthquake was the most powerful in history?

According to the U.S. Geological Survey (USGS) National Earthquake Information Center (NEIC) there are over a million earthquakes each year around the world -- that's on average 3,561 per day or 2.5 per minute. Only a portion of these are recorded (~20 - 30K per year) because most occur over remote areas or in the ocean.
The NEIC collects records for earthquakes world-wide and makes available lists of earthquakes by region, year, magnitude/intensity,etc.

To see list of more recent (or historic) earthquakes visit USGS Earthquake Hazards Program.