In my quest to somehow get 3D polygons to actually plot, I came across the following script (EDIT: modified slightly): Plotting 3D Polygons in python-matplotlib
You have to use Poly3DCollection instead of PolyCollection:
from mpl_toolkits.mplot3d import Axes3D
from mpl_toolkits.mplot3d.art3d import Poly3DCollection
import matplotlib.pyplot as plt
fig = plt.figure()
ax = Axes3D(fig)
x = [0,1,1,0]
y = [0,0,1,1]
z = [0,1,0,1]
verts = [zip(x,y,z)]
ax.add_collection3d(Poly3DCollection(verts), zs=z)
plt.show()