Number please. Anyone calls out any card, and the deck shows that it knew this card all the time
Vernon's Out of Sight, Out of Mind, updated.
I am Spartacus. Five spectators claim to be Spartacus, but you identify the real Spartacus, in spite of not knowing who is lying.
Whatever you choose, you're bound to lose. The 3-card Monte (a Queen and 2 Jokers) in the hands. The cards change, then become two, and in the end you're left with only a pair of Aces.
Spell check. A spectator who loses her card can always find it by spelling her name.
Homer. You show how to beat the hacker - by using homing pigeons.
HASTERIX. A telephone effect in which it's the spectator who writes the prediction.
Monolith. You search throughout the entire solar system, to find the Galactic Federation's hidden card.
Birthday presence. Four strangers use their birthdays to select cards, and find that all the other cards are blank.
The China syndrome. Spectators freely pull cards from a shuffled deck. Your medium unerringly identifies them all.
Make a wish. Two people find they have chosen identical cards from different decks. The two selections then change places while still in their hands.
But there's more. You show that you can memorise a shuffled deck in five seconds.