One popular approach seems to be the gross-out.  Pumpkins puking pumpkin guts, nasty, mildewy pumpkin teeth, secreting orifices.  You know.

If you've got a lot of time, are really bored, or have been blessed with freakish pumpkin carving abilities, you can always go the intricate route. 

Maybe it's because small pumpkins, squashes, and gourds are so abundant this time of year, but cannibalism is always a popular theme.  Pumpkin on pumpkin crime.  It's a shame.

If you're feeling a little wild, you can always opt for something inspired by the animal kingdom.  The nation's number one threat?  Bear jackolanterns!

Finding the traditional jack-o-lantern a little boring?  Try for something bizarre, like a disgustingly large burger or a beached giant squid.  Yum!

When all else fails, simply tack on some appendages to your pumpkin.  Limbs on things without extremities are always entertaining.