Many agencies are working to bring relief to the people living near the Indian Ocean. The WorldCAD Access weblog recommends MCC.
The Mennonite Central Committee (located in Canada and USA) works with local agencies, as well as delivering practical support from North America. In addition, the MCC organization has very low overhead, which means more aid reaches those in need.
World Vision has a list of ten DOs and DONTs -- of what aid works best and what doesn't help.