Well as far as infantry goes...

Recon teams,
Machine gun teams,
Grenediers,
storm troops,
Snipers,
Anti tank,
Flame thrower teams,
Special Forces

And thats all I can think of... Oh yes. Artillery Observers.

As for the tank problem... There might have been a french tank or something with 2 turrets... The Crusader MkI had a main turret and a small machine gun turret on the hull. And the M3 Lee tanks had a main gun in the hull. A secondary gun in a turret and a machine gun in a turret on top of that. So there you go.

Standard Infantry is tricky as there is no such thing.  All of the major combatants of WW2 used quite a variety of differant classifications of foot troops. But however it is classified the classification usually just refers to the transportation employed ie:-

Infantry, Motorised Infantry, Armoured Infantry, Parachute (Airbourne Infantry).

All of the above were troops whose role was to fight on foot using small arms. 

The basic organisation at this time was:

Squad > Platoon > Company > Battalion > Brigade > Division > Corps > Army

But when you get to Division or above you will get support arms of various types (eg artillery and recce elements) thrown in just to confuse the issue.

WW2 caused massive tactical advances in the use of the "specialist troops" such as pioneers, commando's and parachutists and libraries have been written on these units.  Specialist troops such as flame thrower users in the US system (correct me if I'm mistaken American people) tended to be grouped together in a heavy weapons company within a standard battalion. Or a heavy weapon platoon within each company I forget which. Sorry.

Good sources for a basic overview tend to be books written with wargamers in mind.  They tend to have plenty of detail and emphasise the tactical reasoning for the existance of "unique" troop types.

Will

I've Always found the 'Britannica.com' Normandy site very interesting and useful.
I just pop 'Normandy' into google and it coms up in the fist 4 or 5 options.

In the 'Weapons' section of the site there is alot of info. I recall finding my way to a particular part of that site (or maybe a link) that gave a breakdown of all the different types of 'Divisions' during WWII, of the diffrerent Armies etc.
It gave marvellous detail as far as what was included in the different types of divisions, right down to 'how many .45 Colt Semi Auto handguns in the 2 different American types of division (Triangular and Square).

I think you may find the whole site, and that particular part I got to (if you can find it) very useful. It also has alot of 'interactive' maps and diagrams of attacks and positions etc.

P.S. If anyone does know the location of that 'detailed  Division' site or page I'm talking about, please give me the link.

If you're looking for tanks in WWII, some of the Main Battle Tanks landmarks for each country...

Germany...

PzIId
PzIIIn
PzIVd
PzIVg

Panzer A, D, and G models

Tiger
King Tiger

USA

M31 Walker Bulldog

M4A1
M4A3
M4A3E8

M5 Stuart

M26

Britain

Matilda
Centurion
Cromwell
Firefly

Sorry, I'm a bit weak on the Brits, but any of these tanks were significant points in tank development.

What about the Churchill!?  How can you forget the Churchill!? OK, I know nothing about how useful it was, but it's one sexy tank! Even better than the T-35, M3, M4 or Kingtiger!  Then again I also think the Corsair's better than the Mustang or Spitfire... This is getting very interesting.  Before I know it, I won't just be interested in the Air Forces any more.  Wouldn't that be a concept!

A dodgy gearbox LOL.

Will

I was going to jump in with a "how could we be overlooking the T34" but Ivan beat me to it.

It certainly was the first, and probably only, tank in WWII that really gave the Germans a lesson in getting blown up!