How best to help?

If you're looking for ways to assist people who are suffering as a result of the Tohoku quake and tsunami, you can find a healthy online debate about how, and even whether, to act. Common sense tells us to resist the heart's desire to physically go to the scene; better to give funds to those who know how to organize and manage the relief effort.
An organization that knows how to respond is the Red Cross. Some have expressed concern that not all funds donated in the U.S. will reach Japan. Donations to the Japanese Red Cross Society will be allocated 100% in Japan.
Keep in mind that the Red Cross typically directs its efforts in two ways: first, they send teams to the area to provide emergency food, supplies, medicine and shelter. Second, the Red Cross makes cash donations to the victims. In ensuring this second process is equitable, the Red Cross takes time to understand the situations of individuals. Do they do the second task quickly enough? A discussion can be found in yesterday's Los Angeles Times.
The GiveWell Blog has published an in-depth study of the relative merits of giving to various agencies, and concludes giving to Doctors without Borders is one of the best ways to ensure funds result in direct benefits to victims.
Peace Boat is a Tokyo-based nonprofit that has experience in organizing relief efforts, and is accepting donations as well as volunteers in support of its work in Miyagi prefecture.
Rebuilding and recovery will take years. Architecture for Humanity focuses on long-term, carefully considered design and construction, and publishes its objectives and plans, so it can be shaped and perfected over time by comments and suggestions. AFH has a team and a preliminary plan in place. If you are in this for the long haul, this is a great place to consider donating.