Here are some sources for news and analysis on the nuclear events in Japan to consider:
Areva’s analysis as of April 1
International Atomic Energy Agency
Wikipedia’s entry for the Daiichi nuclear crisis
Japan’s Nuclear and Industrial Safety Agency
Germany’s Federal Ministry of the Environment, Nature Conservation and Nuclear Safety BMU (site includes spent fuel bay inventory and thermal power estimates)
Japan’s Ministry of Education, Culture, Sports, Science&Technology publishes radiation data here.
The New York Times maintains an updated chronology of major developments here.