Disney Mega Variations :)
We'll start with an easy one and go from there.
Duck Nephews or Duck Child or Huey Dewey and Louie, you choose.

Duck Child

These little guys will just have dots for eyes and the eyes are part of the head mold. One should note that only the blue and green hats were available, no red. Poor Huey.
Duck Child or Dewey and Louie? You got me.

These guys are kind of the "middle of the road" guys. They do not have the eyes as part of the mold, but the eyes are much smaller than the currents below. They are on 3.9 stems with thin feet.
Huey, Dewey and Louie

Finally we get to see Huey and his red hat. This set is on the older Yugoslavia stems and this set...

is on the newer Slovenia or Austria "color coordinated" stems.
Donald Duck

If I knew how to spell plethora I'd use that term as this guy is OHmazzing! Shown is an older Donald, Donald Softhead, the recently discontinued Donald and the latest version with the big mouth. Just the recently discontinued one has a few Variations of his own.
Different?

Sure, maybe just stem markings and thumb tabs, but different. Some of the eyes are different shades too. What do you mean that doesn't make them different? Hey, it's my page. They're different :)
Hair of feathers?

Then we must consider all the differences of the older Donalds such as the differences in the molds. Can you see how the one on the right has feathers with more detail?
Like I need a hole in the head...

There are many different head molds. Shown here (from left) is a plastic hinge pin, metal hinge pin and a plastic hinge pin with an extra hole. Why the extra hole? Because this guy doubled as Scrooge and that upper hole was for Scrooge's sideburns.
Add all that up and add country of origin, patents, feet vs. no feet and what have you got?

A splitting headache. If you want a worse "pounder", check out the Variations discussion that was done on Pezheads. Click here, or go back to the Variations section on my homepage.
Die-Cut Stem

Here's a Die-Cut Stem. It is actually cut from the stem so that the yellow inner sleeve shows through. Other Die-Cut stems include Bozo, Casper the Ghost, Easter Bunny, Mickey Mouse and Comet.
Goofy Guy

The main differences in these guys is the teeth, ears and nose. Let me explain...
Teeth...

The one on the right has teeth that are removable from the face and are not part of the head mold like the one on the left. There is one on my wish list that has a nose that is also removable. Too cool!

Here's a shot of three with removable teeth( well, if it wasn't for the glue, that is). Notice the different head colors, pale pink, flesh and pink.
Ears...

The one on the left is the non-movable version. The ears are part of the hair and don't move. They're pliable, but don't move back and forth. The one on the right has ears that are separate pieces of plastic and they move back and forth. Note the different hat colors too.
M-I-C...K-E-Y...M-O-U-S-E...

Look at Minnie. She likes Mickey. Shown is a Mickey with Die-Cut face, Removable Nose, Poke Through Nose, the recently discontinued and the latest and greatest with his gal.
Hinge holes

Once again there are many different head molds. Shown above are some examples of different hinge holes of three Removable Nose Mickeys.
Nose

Here's an example of a Removable Nose versus a Poke Through Nose. The Poke Through has a face piece that is similar to the Mickey with Die-Cut face.
Add it all up...

and you get another fun dispenser for variations. All the above are different in some way or another.
Pluto

Here are the three different Pluto styles. From left is the "Original", recently discontinued and the current version. The recently discontinued and the current are pretty simple, but the Originals are tough.

Here's a shot of four different head molds. Minor differences, but definitely different molds. There are about 9-10 different head molds. For a more complete description, check out the Pezheads discussion on this Variation. It is a great resource. Click here for Pluto, or continue to check out the rest of the Disney.
One more thing...

Here's a shot of one of the Plutos above. Look below the country of origin. See those little "Half Flowers"? These will only be found on the 2.6 Patent, Yugoslavia stems.
Practical Pig

I'll let you decide if there are two or three different Pigs.
"A"

This guy is somewhat evil looking. He's got the pointy cheeks and ears and a flat cap.
"B"

This guy seems a little more happy and easy going, and has a wavy hat. Sometimes he comes with whites of the eyes, and sometimes he doesn't.
"C" or Remake "A"???

The one on the left is the most recent issue, but it's the same mold as the first of the litter. And with those eyes, he's even more frightening than the first guy :O

Here's another shot of a DBP Patent (Deutsches Bundes Patent) from the guy on the right.
Zorro! "Z"

Finally we come to Zorro. Again, a gold mine of Variations. Some things to look for would be the mask...

Either straight or arched...

Different copyrights...

And especially look for the one with the Logo on the stem...

Rob, this truly has been the happiest place on Earth. Now take me back to reality!