SOSO made a windows display for HBO back in 2009 that was rather inventive. Using an Arduino controller they were able to create an interactive art project that would blow fake snow in the wondow depending on where a pedestrian on the street in standing. IR sensors were placed along the front of the window to detect objects passing by. The Arduino would then turn on fans that were at that location and shoot the "snow" into the air. The board would also sense cars in the street and change the background color due to cars on the street. Although source code isn't available for download, the concept isn't anything new. But perhaps the video will inspire something new from you.
Cabe