Ouch BikeChick, I HATE blisters.

I've had very good luck with the Band-Aid Advanced Healing blister pads. It seems a little counterintuitive (to me) that something that thick would help, but they really do, IME.

If your blister is bigger than that, you might try Tegaderm, which is great at eliminating friction, but I haven't always been able to make it stick on my feet.