The situation after a disaster can be chaotic, with a rush of international, national, and local aid agencies as well as individuals trying to help.
Only fund those that already have an office established in country because of the amount of time and money it takes to get anything more than just search and rescue up and running. Those with an already established presence will know the people and systems better and be able to work more quickly and less expensively.
Laura Freschi of AIDWATCH has a few suggestions for donations.
This is a hard time to be thinking about giving to charities, and no one needs to feel guilty for not being able. But please, if you are able, give from your heart.