I stock up on Compeed whenever I visit my family in Germany. It works like a charm. Not only on blisters, but any cuts or scrapes where you don't really want to rub anything over it (such as a sock). It is waterproof and has some substance on it that helps healing. I leave it on until it falls off by itself.
A quick alternative, while not quite as nice, is duct tape. Poke the blister open, cut off the skin, let it dry, disinfect with alcohol (or something else non-greasy) and put duct tape over it - big enough so that when the edges rub off the skin a little bit, the blister is still well covered. It can't stay on as long as Compeed (or the Band-Aid version) because it doesn't let air through, but if you have 10 miles of hiking ahead of you, yeah, it helps
