Among the world's most cost-efficient and effective international relief organizations is Lutheran World Relief. I would say this whether I were a Lutheran Christian or not. For years, LWR has been recognized by any number of organizations and publications as the world's best-run charity, its effectiveness and range of activities being disproportionate to the numbers of Lutherans comprising the world's population.
So, as you consider where to donate monies to go toward bringing relief to the many effected by the recent Indian Ocean tsunamis, you might want to consider a donation to Lutheran World Relief.
Here are relevant links:
Lutheran World Relief
LWR information on relief efforts already happening: here, here, here.
Page on which you can make contributions.
Another good relief organization is World Vision.
Let me hasten to add that I have no personal connection with Lutheran World Relief, apart from my denominational affiliation. But through that "connection," I have received frequent reports of the organization's activities. That's why I feel so comfortable in recommending it as way people can financially respond to the needs of the victims of the recent tsunamis.
The congregation of which I am pastor sponsors a young Zimbabwean child through World Vision. I also have a high regard for that organization.