You need some autumn-colored cardstock, patterned paper and white paper, along with ribbon [or twine, which I used] and clothespins. I got the pumpkins at Michael's last year. You could buy them using the 40% off coupons they offer every few weeks.
Cut your solid-colored cardstock to the finished size and then glue a slightly smaller piece of the patterned paper onto it. I added an even smaller piece of white paper and wrote my letter onto this. If you don't like writing, you could use a stencil or sticker instead. All you need to do now is hang your ribbon/twine, pin on the letters and attach the pumpkins!
This would also work great on a mantle and could be made to any size you choose!
Now I'd love to hear about your fall decoration inspiration!