I got stalled on this because I didn't know which charity was best suited to help out with this. My criteria for this sort of thing are low administration costs, good connections on the ground in the impacted area, and good judgment about how to spend the money.
The answer to my question came in an article that I spotted in the Seattle Times on Christmas day: Richard Berger of West Seattle. Berger had a desire to help out, and came to the conclusion that the thing that would do the most good is survival blankets. He has managed to raise over $100,000 to send about 110,000 blankets to Pakistan.
The principal charity that Berger is working with is the Mercy Corps, based in Portland. Only 8% of the donations they collect are used for administration, which is very good.
Article from the Utne Reader: Blanket Relief
Story from the Mercy Corp site: Blanket Campaign Warms Survivors
