Molecule Madness by Graham Hey

Two cards (2 x Queen of Spades) are shown to a spectator, who is then handed an "invisible card" the 9 of Hearts. The spectator throws the invisible card towards the magician who is going to catch it between the two queens. The spectator does this and the 9 of hearts instantly appears between them! Then, whenever the magician wants, the 9 of hearts vanishes - only to turn up in another location. This is a great self-working effect that gets great reactions.

You'll need to make the gimmick with a couple of things most magicians will already possess. It'll take you just five minutes and requires a tiny bit of arts and crafts.

The PDF contains written instructions and links to perform and construct the gimmick.