Basic Units 8available to everyone):

Basic Infantry
Basic Fighter
Basic Bomber
Basic Destroyer
Basic Cruiser
Basic Battleship
Basic Battlecruiser
Basic Carrier
Basic Submarine
Basic Mot. Infantry

Germany:
Wehrmacht (basic infantry unit)
Waffen SS (some kind of "Special Forces")
Fallschirmjäger (elite airborne infantry)
PzKw I (light tank)
PzKw II (basic light tank)
PzKw III (basic medium tank)
PzKw IV (medium tank)
PzKw V (medium tank, later)
PzKw VI (heavy tank, later)
PzKw VI Tiger 2 (heavy tank, later)
Panzergrenadiere (mot. infantry)
Me-109 (basic fighter)
He-111 (basic bomber)
Ju-87 (unique german unit)
Fw-190 (improved fighter, appeared first in 1941, later)
Me-262 (jet fighter, later)
Ju-88 (medium bomber, ?)
88mm FlaK/PaK (unique german artillery)
sIG 33B/StuG (self-propelled artillery)
StuG 42 (self-propelled artillery, later)

Italy:
Basic Infantry
Militia (unique italian unit)
L6/40 (basic light tank)
M11/39 (basic medium tank)
M13/40 (basic medium tank)
Basic Fighter
Basic Bomber

Turkey:
Basic Infantry
Basic Fighter
Basic Bomber

Spain:
Basic Infantry
Republican Guard (unique spanish unit ;-)
T-26 (basic light tank)
BT-7 (basic fast tank)
T-28 (medium tank)
T-34/76 (basic medium tank)

USSR:
Red Army (basic infantry unit)
NKWD Troops/Red Guard (some kind of "Special Forces")
Siberian Troops (hardened troops, special winter warfare equipment)
T-26 (basic light tank)
BT-7 (basic fast tank)
T-28 (medium tank)
T-34/76/81 (basic medium tank)
KV-1/2 (heavy tank, later)
JS-1/2/3 (basic heavy tank, later)
SU-100 (tank destroyer)
Polikarpov I-16 (weak fighter)
Yeak-1/3/9 (basic fighter)
Pe-2 (bomber)
Il-2 Shturmovik (basic medium bomber)

France:

Great Britain: