The very talented Leo Dias has a handy tutorial on creating killer zombie makeup using very simple materials. You'll find the first part here and the second over here , with text in both English and Portuguese.
A zombie walk participant enjoys a quick snack.
One of Leo's insanely detailed urban zombie resin masks surrounded by various appliances and makeup supplies.
The basic technique using liquid latex can be adapted for a multitude of applications. One of the great things about it is the built in success rate. The first time you do it the results will be good, and the makeup will just look better as you get more experience.