Holy Water... and Oil by Fenik
The effect is as clean as it can get. Three red cards are mixed amongst three black cards. The performer waves his hand over the mixed packet and the black cards are magically separated from the red cards. This happens three times in a row, each time looking more impossible. Everything flows smoothly along until POW! You knock them out with the climax.
Download the video, learn the routine, and stun your audience!