A lot of people want to help out the Japanese people who are handling the disaster and nuclear crisis with extreme calm and dignity (truly an inspiration to the world). I suggest you read this article to get a sense of what the Japanese are like in times like these (via HotAir).
Here are a couple of links you may find useful to avoid scams and find efficient charities:
One charity that I’ve seen recommended is the Salvation Army. I understand that they have people on the ground in Japan and are known to be highly efficient with the money.