Japan until a few weeks ago was the second largest economy on the planet. They don't need your donations.

Here's what's going to happen if you text "Takemymoney" to the Red Cross.
They will get your $5, and it will sit in a bank account forever.
There (at last count) was still $1.1 BILLION sitting in NGO coffers from the Haiti earthquake, because these NGOs aren't able to mobilize enough people to actually use all the money.
Instead of throwing $5 at it, wait and see what Japan comes forward and says they actually NEED. Cash up front will help mobilize some rescue and support efforts, yes, but a glut of it doesn't do any good in the long run.