Google sure makes cooking easier! This baking powder "recipe" saved my chocolate chip waffle breakfast for the kids this morning. :)
1 t baking soda
2 t cream of tartar
Mix and use. (If you want to make some to have on hand, add 1 t cornstarch to keep moisture away.)
I also used this recipe to make cream of chicken soup for a casserole tonight. Very easy and much healthier than the canned stuff.
Here's a great resource for other substitutions, too.