Nothing to fear...

Batman

A Variations Field Day. With feet, without, 2.6, 3.4...some of my psychotic examples below...
Old Small Ears

Original vs. Remake?

This is a shot of the copyright on the Blue Small Head Batman. The one on the left is marked "Sign Nat'l Periodical Pub's Inc" and will be found on the "Original" (older) Batman. On the right is the same style Batman, but has "DC Comics INC 1985" marked on his hard blue head. The black version of the Remake is always marked with "DC Comics INC 1985". Both have been discontinued.
The new guy in town

Dark knight. There are two variations of this guy. The first that was issued had very pointy ears. This might have been dangerous to "Junior" so they came out with the second version and he has ears that are rounder. It's a kinder, gentler kind of Batman/Dark Knight. The best way to see the difference is to look them straight in the eye...

The Softheads

Superhero "Softheads" from 1978-79. The only variation to note with these guys is that some have heads marked "Hong Kong" and "DC Comics" and some have only "DC Comics" stamped on the back of their rubber type heads (pictured below). Another tidbit to know is that the stems of these and other "softheads" are almost always marked with the 3.8 patent number and "Made in USA", but some 3.4's are known to exist, as well. From left is Batgirl, Wonder Woman, Joker, The Penguin and Batman.
Batman Softhead

Pictured here are two examples of the Batman Softhead. The one on the left is marked "Hong Kong, DC Comics, 1978" and the one on the right is marked only "DC Comics, 1978". And the faces do have some minor differences too.
Joker

What a cool looking dispenser! From left is "Hong Kong, DC Comics, 1978" on a blue stem, "Hong Kong, DC Comics, 1978" on a yellow stem and "DC Comics, 1978" on a blue stem. Stem colors can be fun too!
Three different variations of Captain America

Flesh face Black Mask Club Med
Wonderful Women

Current, Raised Star with feet (Yugoslavia and Austria), Raised Star no feet and a Softhead.
The big difference in these "Wonderful Women" is that the older varieties have a "Raised" Star on their heads. The newer version's head is smooth. Here's a close-up.

Incredible Hulk!

The "Cranky Looking" Hulk is similar to many of the Superhero series in that it has an "Original" and a "Remake". The two on the left have the larger head are are called Remakes. The others are Originals and came in two different colors, Light Green (thin feet 3.9 and NF 3.9) and Dark Green (3.4 and 3.9). The two Remakes shown are a 4.9 with thick feet and a 3.9 thin feet. What are thick and thin feet you ask.

The thin feet are "breakeeeee".
Spiderman

Current, Current with "thin feet", removable eyes with feet, removable eyes no feet (two shades).
The way to tell age on these dudes is to look at their eyes. The older ones have removable eyes and the newer ones have eyes that are molded to the head.

The one on the left is the current and has eyes that are part of the head mold.
There is another version that eludes me. It is a test mold that does not have the "webbing" on the back part of the head, and numerous versions of it! As they say at conventions, "Very Rare".
A couple more Heroes...

Green Hornet and...

Thor!
To the Bat Cave Robin!