Death ray?
I'd love to see a Death Star model made, with some sort of acrylic/optic/crystal/quartz/lens to "focus" the beams.. lol...
Laser/light graffiti? Build a rig to draw on a large surface from your mysterious black transit van? Naturally, we don't want to do this on apartments or occupied offices with windows - that could lead to some trouble.
Laser harp/other musical instrument always sounds like a cool idea. Although you probably want visible beams for that (or maybe you don't - it might be cool to have "nothing" to wave your magic-MIDI-controlling hand through)