Falling leafs, snowflakes, flowers or wathever you want :). Demo video

And there is a Pro version of this plugin, with many additional features:
– choose which object fall (custom and multiple icons allowed)
– quantity of objet falling
– speed of the object (can be random speed)
– 3 possible trajectories
– define on wich pages or custom urls the falling things appear
– define on wich period the falling things appear
– multiple profils (ie: one for summer and one for winter)

More informations and demos here