To accomplish the effect in the first photo, you only need sticks or stray branches from your own yard, and some time and creativity to carve your pumpkins. You could scatter some fallen leaves as well. The birds are fun but totally optional.
The second look is pure genius: photocopied black and white portraits from history books or encyclopedias. Mount them on some black poster board and display them, clustered on shelves or mantelpieces.
And the third photo is so effective because the pumpkins--aside from being so artfully carved--are different shapes and sizes and clustered together. You don't need two dozen pumpkins of your own to create this effect. A carefully chosen few would have a similar, spooky look.