I know a lot of people are short on cash right now post-holidays; while there will no doubt be an ongoing need for cash for quite a long time to come, in the immediate future, you can donate your unused airline miles to the Red Cross and others.
Please be wary of giving money to religious-affiliated organizations in South Asia. Many are perfectly fine, but some are essentially fronts for groups which advocate communal violence. As noted previously, if you do want to give directly to a locally-based relief organization, I recommend Sarvodaya.
American Institute of Philanthropy has a page listing tsunami-related charities they have vetted in terms of financials -- money actually going to the cause, rather than to more fund-raising, which is the other thing to worry about in making choices about where to donate. My personal preference here is for Doctors Without Borders.
Send cash, not goods. As the AIP web page tells you: The best way to help is by sending a check. Cash donations enable charities to buy the most needed type of food, medicine, clothing, shelter materials and other supplies. By buying relief products locally or regionally, charities can reduce shipping costs and more rapidly deliver assistance. Before sending any goods, first contact the charity to find out if they are appropriate and if it will be cost effective to distribute them. For example, during the Bosnian War (19921996), 37.5 million pounds of inappropriate medicines were donated.
And finally, from a list: "On Marketplace (public radio) today, they were talking about corporate giving to help with the disaster. They said Pfizer is giving $10 million cash, and $25 million in medical supplies, thereby matching the dollar amount pledged by the US government. Seems like the US ought to be able to do better than a single corporation. Congress is supposed to be talking about an aid package next week; might be worthwhile to drop a note of encouragement to our representatives."