I've always liked putting together my own spectacular decorations out of ordinary stuff from the local Halloween store. There are a couple of outdoor decorations I've done that have turned out particularly well.
The first one is the "Car From Hell."
All you need are five or six of those fake fire pots (the kind with a fan blowing up at the orange-lit cloth), some sort of near-life-size creature (a regular plastic skeleton works great), sufficient extension cords and power strips, and a car you can arrange to keep parked as part of the decoration.
Setup is quite simple -- park the car somewhere visible and run an extension cord out to it. (Try to make the cord hard to trip over -- trick-or-treaters will be coming through, after all.) Place the firepots around the interior of the car and put the skeleton in the driver's seat. You're done.
The "car on fire" effect is quite startlingly realistic at night, at all distances from up close to all the way down the block. And even a cheap skeleton looks great in the flickering "firelight".
(I got the idea from here
. His pictures don't really do the concept justice -- it looks truly spectacular.) I know that using your car as part of the decoration is likely to be a sticking point, but even if you only leave it up for the duration of a Halloween party, the effect is well
worth the setup effort.
The second decoration is a rather more subtle effect which (for obvious reasons) only works at night. All you need are some black helium-filled balloons, a glow stick, and some fishing line.
Again, setup is simple. Tie several balloons (you'll need to experiment a little to figure out how many you'll need for the necessary lift) to the end of the fishing line, and attach the glow stick to the line, at least ten or fifteen feet below the balloons. Then just play out the fishing line as you let the entire assembly float up well above the rooftops and treetops. Anchor the line somewhere and you're done.
And so you have a glowing... SOMETHING hovering high overhead, gently weaving and bobbing. It doesn't look or move like anything that people are accustomed to seeing in the sky, and it's visible for quite a large distance. Is it a ghost? A fairy? A UFO? Expect curious onlookers from all over the neighborhood coming by and trying to figure out what the Hell it is. And if you have several of them, at different colors and different heights, it starts looking really
(The reason for hanging the glow stick so far below the balloons is simply to separate them. The balloons are less visible, but more readily identifiable once spotted. Keeping them separate means the eye is only drawn to that lone glowing THING hanging in the sky.)
There are, of course, plenty of variations on the theme. Some people have had good results putting the glowstick inside a white balloon to diffuse it a bit. (In my testing, I found that dimmed the light too much, but your taste may vary.) If it's cloudy, gray balloons might be less visible against the sky than black. And if it's too windy, call the whole thing off or the line will just get caught in the nearest tree.