It's always best to donate to well established organizations like the Red Cross. The Red Cross in China says survivors need food, water and clothing but they are asking that people don't send that overseas. Instead, the Red Cross says money would be a better donation. That way, supplies can be purchased and distributed to the victims in bulk.
If you are in doubt of donating to a particular charity, you can always check with the Better Business Bureau. Just click on the link below.