After much hemming and hawing, we selected the ol' cups-full-of-water-stacked-in-a-pyramid-blocking-their-front-door prank for the neighbors. I think they liked it. My informal neighborhood survey tells me that neighborhood morale has increased several points in the past two days, and I can't help but attribute the increase to some great pranks.
notice the water on the ground in this picture--we did have a slip-up and knock over about half of the tower at one point. lucky for us, the family's two dogs said nothing, no alarms went off, and we were able to complete the project.