I found this idea in a Martha Stewart magazine a few years ago and have decorated for Halloween this way ever since. I prefer to keep my decorations a bit low key and it is hard to find "classy" Halloween decorations, but I think this is a good compromise between the spooky and the tasteful.
Gather some large, twisty branches and anchor them to your front porch area. You can tie them to a pillar as shown, or cut a hole in a large pumpkin and stick them into the top using the pumpkin as a base.
Collect several types of spooky black birds. I have many sizes of vultures and crows that I found at Joann's and the Dollar Tree. I also had some random birds around that I spray painted black.
Spread some cobwebs on to the ends of the branches and cluster jack o lanterns around the base. I replace my regular porch bulb with a purple one and it looks especially creepy at night.