NZPA has an article on NZ Red Cross dealing with claims it is not spending tsunami money quickly enough.
NZRC correctly points out that spending all the money immediately may do less good, than some long-term expenditure such as building new houses and shelters. They also point out that Red Cross ring-fences any interest gained on the donations so it is all spent on the cause donated to, in the end.
Red Cross is not perfect (and US Red Cross has some issues certainly) but having worked for them for four years I can say they are one of the safest disaster relief charities to donate to. Unlike many others they don’t deduct any marketing or admin costs from donations tagged to a specific disaster, and the Int Red Cross does the same, so $100 donated is basically $100 spent on the ground.
They also have an advantage of having local societies in every country, so relief is controlled by Red Cross and Governments are not able to embezzle and squander it so easily. And unlike some they have no religious agenda with their relief – it is purely done on a humanitarian basis.
So not perfect by any means, but in my eyes the best choice when wanting to help out. I put SCF not far behind – they tend to also be highly ethical.