The Birthday Deck - Dynamic FX
Brilliant idea, where you have a deck of cards made up with numbers and months of the year.
You meet a spectator, and reverse some of the cards in the pack. Now, and only now, does that person tell you their birthday.
Spreading through, you reveal that you reversed the EXACT cards to make up their Birthday!
Booklet is old and a little tatty, but the routine and effect is KILLER!