Disasters like the one in Japan remind me that I am fortunate to have a food, water, and shelter. No matter how challenging things get for me, I am still in a position to help others. Because I am not able to volunteer or give blood, I donate money. Even $10 can make a difference.
Here are some organizations that help people in need (the US organizations have international counterparts):
American Red Cross: http://www.redcross.org/
Doctors Without Borders: http://www.doctorswithoutborders.org/
Oxfam America: http://www.oxfamamerica.org/
In addition to helping people in Japan, these organizations are working on relief efforts in North Africa and the Middle East, Haiti, and other projects throughout the world. If you prefer to help those in need in your own country, there are plenty of local charities that accept donations.
Before you donate any money, make sure you are donating to a legitimate organization. Please do your homework. Watch out for fake charities. Here's an article that gives advice about making donations: "Donate to Japan tsunami victims, not scammers: How to avoid frauds set up to snare charitable dollars aimed at Japan." Even though the article is directed at Japan programs, the information can apply to any charity.