Fake foam or plastic pumpkins are abound in craft stores and now is a good time to pick one up. They come in orange, white, black, and chalkboard at Michaels. You can leave it plain or give it a makeover with dripped crayons (rainbow on a white pumpkin is great, but black/silver/gray or Halloween colors would be great too), adding craft ribbons or bows, adding a glow-in-the-dark treatment, covering it in fake gems, or painting it to match your decor.
I re-pinned this idea onto my Halloweentown Ideas Pinterest board a few months back and I still absolutely adore it. A stuffed pumpkin made out of a rich, fall-like fabric is a great option and a good way to spend a rainy afternoon. Here's a tutorial from HGTV for easy sewn pumpkins which can be done in velvet, burlap, cotton, or any other fabric you can think of.
Making an origami pumpkin is actually super simple and you can do it with any kind of paper. Patterned scrapbook paper is a wonderful way to add a Gothy touch or to match your own home decor. For a simple tutorial, check here on Origami Instructions.
Mercury glass is a very pretty material that works especially well for Halloween decor. Something about the reflective but distorted surface is a really refreshing take on the traditional orange pumpkin and great if you're not crazy about incorporating tons of orange into your Halloween look. This one above is from Pottery Barn, or you can look here for a tutorial on adding a Mercury-Glass look to any glass.
If you want an alternative to a large pumpkin but you want something organic still, consider buying a turnip to carve! Turnips are more traditional in certain places and are much more space efficient. For a turnip carving tutorial, check here on Makezine!
Do you prefer real pumpkins for your Halloween decor, or do you add in fake ones as well?