This is the best way to visually interpret current data from the reactors at Daiichi. This tool uses the 6 hour CSV data from TEPCO and puts it into a graph format so you can detect trends and changes. The page is in Japanese but translates with Google Translate
Some other updated links for daily or hourly monitoring at the plant:
Monitoring posts at the plant (daily) http://www.tepco.co.jp/en/nu/fukushima-np/f1/index-e.html
Exhaust stack of units 5-6 (daily) http://www.tepco.co.jp/en/nu/fukushima-np/f1/stack/index-e.html
Radiation survey maps (reactor buildings, inside reactors, around plant) updated periodically
Reactor Parameters (hourly, 6 hours) http://www.tepco.co.jp/en/nu/fukushima-np/f1/pla/index-e.html
The latest Daiichi reading update directly from their releases by TEPCO whenever they post new numbers.
Due to file size and other factors these are displayed in a new browser window.
Launch the latest readings.
TEPCO has stopped sending this data.
There is some ongoing data made available but most is in fairly static formats.
Newest monitoring post radiation readings: http://www.tepco.co.jp/nu/fukushima-np/f1/index-j.html (In Japanese but translates with Google Translate)
Newest reactor parameters: http://www.tepco.co.jp/nu/fukushima-np/f1/pla/2012/images/table_summary-j.pdf (In Japanese but readable if you are familar with the format)
We do have an archive of all the reactor data up to March 15, 2012.
It is a CSV format available for download as a zip file.