For about an hour i've been decompiling all the Minecraft Classes and i (think) i've found all the mob classes. If you wanted to make a new Minecraft mob or study a certain mob's code, you can easily find all the mobs now!

To get to the classes, go to C:Users(your username)AppDataRoaming.minecraftbin and into your minecraft.jar

How to decompile the classes to look into them: I use DJ Java Decompiler (which you can look up on google)

mo.class - Chicken
mp.class - Cow
mr.class - RedCow
ms.class - Ozelot
mt.class - Pig
mu.class - Sheep
mv.class - Snowman
mw.class - Squid
mx.class - Villager Golem
mz.class - Wolf
nd.class - EnderDragon
nm.class - Blaze
nn.class - Cave Spider
no.class - Creeper
np.class - Enderman
nr.class - Ghast
ns.class - Zombie
nt.class - Magma Cube
nv.class - Pig Zombie
nw.class - SilverFish
nx.class - Skeleton
ny.class - Slime
nz.class - Spider
oa.class - Zombie
od.class - Villagers
og.class - Humans (says Notch in the class file)
pl.class - Villagers