The other night I made these paper hearts while watching TV. You could stick them on a wall or door temporarily, or glue them to a board permanently to make a 3D wall poster. They'd be cool to attach to presents, too. Surprise somebody with an explosion of hearts!
Download the page of hearts here.
To make a flat heart into something three dimensional, roll the inner edges of the two arcs toward the back with your fingers to get the shape started.
Then stick a flock of hearts to a wall with loops of tape or poster putty placed at the bottom point on the back side of each shape.