Make a "The Works" bomb. All you need is The Works toilet cleaner, some foil, and a plastic bottle. A wide mouth bottle like a gatorade bottle or Powerade will work best. Most sports drinks have wide mouth bottles. Put about four foil balls in the bottle no wider in diameter of the opening, then put a few ounces of Works toilet cleaner in the bottle. Shake hard for five to ten seconds, and get rid of it. It'll take a few minutes to expand, then explode. If thrown in an opened garage, or on a doorstep, the smell, and sound are uncomparable.
You could also try a simple liter sized bottle of diet coke. Pop a few mentos in there. Screw the cap on loosely, hardly at all actually, and throw it. In an open garage, it'll propel itself and knock shit off the wall and dent cars.
Demonstration with 2 Liter Bottle [5.4mb]
Equally effective is simple baking soda, and vinegar. That'll explode a bottle. Take any ol' bottle, and try it a few times to get the proportions right. Perfect for open garages (the smell), or gardens. It'll kill the plants.