What is a better-tasting substitute for baking powder? My wife complains that baking with bakeing power results in a bitter after-taste. We were wondering if there's a good substitute for it that tastes better. We sometimes use beaten egg whites (in pancakes for example) to substitute for the BP, but in drier recipes that might not work so well (like scones) and even in pancakes the results are less than great. 

Any ideas?
You might look at what the specific chemical agents are in your baking powder; it's possible that you have one that uses sodium acid pyrophosphate, which can leave a bitter taste.

Some people avoid the various aluminum based ones, as they can give a metallic taste, but it's likely preferable to bitter.

You can use baking soda and an acid, but it'll then be single-acting (it won't give a second rise when heated), which might affect your baked goods, particularly if you don't get it straight into the oven after mixing.