I believe I mentioned recently that you just can't go wrong drawing zombies. Well, I stand by that assertion.
There's something intensely satisfying about drawing these creatures. Perhaps it's the joy of drawing something repulsive yet fascinating, perhaps it's the fact that you get to be creative with human anatomy, or maybe it's just fun to draw a face so messed up it looks good, at least in a gruesome sort of way.
I don't know what it is exactly, but boy is it fun.