The most important thing is to make sure your money finds it's way to the Japanese people, not into a hustler's pocket. Apple, Google, and the social networking sites have set up ways to donate that I consider safer because they have so much to lose if the word got out that they were operating a scam on the backs of the victims. The article below describes how they work.
http://www.france24.com/en/20110314-digital-ways-donate-japan-disaster-relief