For those work in US, you may also consider to donate through the American Red Cross at
http://www.redcross.org/news/in/profiles/Intl_profile_ChinaEarthquake.html
and click 'Donate Now'.
Especially for those who can get a match from their employers, that will double your contribution.
Also, donation through American Red Cross has tax credit, and you may take advantage of that and consider to donate more.