Felix Salmon offers the case against donating money to Japan. Read the whole thing, I don’t wish to quote it out of context.
For reasons which you can find outlined in my Discover Your Inner Economist, I am generally in sympathy with arguments like Felix’s, but not in this case. I see a three special factors operating here:
1. The chance that your aid will be usefully deployed, and not lost to corruption, is much higher than average.
2. I believe this crisis will bring fundamental regime change to Japan (currently an underreported issue), rather than just altering the outcome of the next election. America needs to signal its partnership with one of its most important allies. You can help us do that.
3. Maybe you should give to a poorer country instead, but you probably won’t. Odds are this will be an extra donation at the relevant margin. Sorry to say, this disaster has no “close substitute.”
It may be out of date, but the starting point for any study of Japan is still Karel von Wolferen’s The Enigma of Japanese Power. Definitely recommended.