In Finder Keeper, you allow a spectator to shuffle and mix a deck of cards. After looking briefly in the deck and considering for a moment, you bring out two cards and place them face-up on the table. You deal cards (face down) until the spectator says "stop." At this point, you insert one of the cards face-up in the deck.
You deal again until the spectator says "stop" and place the second face-up card on top of the pile and then rest the rest of the deck on top. When you browse through the deck, you can show that each face up card is next to its mate in the deck. For example the black fours (four of clubs and four of spades) and red kings (king of diamonds and king of hearts). This one is strong and requires no preparation or changes to the deck or the cards.