One good option is the American Red Cross. Just go to their donation page to donate online, by phone or by mail.

Google.com has links to several ways to donate to help with Tsunami Relief.

You can also donate to the Salvation Army’s South Asia Disaster Fund

However you decide to give, it is important that you give.

Swirling ocean swells are seen along the flooded coast Sri Lanka in an image taken by DigitalGlobe’s QuickBird satellite shortly after the area was hit by a Tsunami on December 26, 2004.