My heart goes out to the people affected by the March 11 tsunami. It is truly an example of the awesome destructive power inherent in nature ... and the need for science to understand the way such power can be released.
More Information on Tsunami
One great resource for learning how a tsunami works is the NOAA Center for Tsunami Research, which has a lot of detailed information on the subject (including this graphic of the energy levels associated with the earthquake and how they spread out from the quake's epicenter).
Source: NOAA Center for Tsunami Research
The NOAA Center for Tsunami Research has a page specifically dedicated to the Honshu event, which features a link to a great (and terrifying) animated video showing the movement of the waves throughout the Pacific Ocean. While this doesn't necessarily offer specific information about the scale of the waves, it is an impressive graphical demonstration of what happened.
NOAA aren't the only ones trying to explain the science behind this devastating event. For example, Scientific American has released an interesting series of articles on the subject, including How Does an Earthquake Trigger Tsunamis Thousands of Kilometers Away? and NOAA map predicts tsunami wave heights around the Pacific rim. (For those interested in more about the nuclear reactor that was damaged, check out How to Cool a Nuclear Reactor ... the sort of how-to article that, thankfully, doesn't come along very often.)
At About.com, we've got some features on the subject as well. Probably the most comprehensive coverage of the disaster is from the About.com Geology Guide, Andrew Alden, in Japan Hit by M 8.9 Quake [updated], with a nice follow-up as well. (And his article, Tsunamis: Killer Waves, is a great overview on the subject.) Our Weather Guide presents an intriguing discussion of the Role of the National Weather Service in Tsunami Events.