Today's 9.0 quake that struck off the island of Sumatra in Indonesia, and triggered tsunamis in Southern Asia, was the 4th strongest earthquake since 1900. Here are the top 5 quakes in that time period:
1. Chile-1960-9.5
2. Alaska-1964-9.2
3. Aleutian Islands-1957-9.1
4. Kamchatka-1952-9.0
5. Sumatra-2004-9.0
Read more about the Sumatra quake in this New York Timesarticle(1).

1. http://www.nytimes.com/2004/12/26/international/asia/26cnd-quak.html