here we go. These were just some quick stuff thrown together in approximately 29 seconds
Bug out! US rule: A lot of US infantrymen were fresh recruits, thrown into battle. Recruits are [insert suitable number] % cheaper to buy, but if fired upon, and the squad has not reacted yet, roll 1D6. On a roll of 1-2, the squad bugs out, and moves its full move away from the firing squad. On a 3-6 they may act normally.
Walking fire! US rule: US troops often complained about being low on ammo, when they reached the point that their German or Soviet counterparts entered battle with. Once per game, a US squad may conduct walking fire. Advancing, while unloading a steady hail of bullets. This allows you to spend both actions moving AND shooting. This fire is always considered to be in cover (if the target is already in cover, no casualties are inflicted). However, double the attack dice for suppression purposes.
Mission tactics!: German rule: German troops were generally briefed on their own objectives, as well as those of their immediate superior. German units never suffer a penalty for loosing their squad leader.
Soviet special rules:
Soviet squads may NOT be split into teams. They operate as a single entity.
Tenacity: Soviet troops tend to be extremely rugged, as well as excellent users of camouflage. USSR infantry receive an armour roll of 6+, if they are in cover or more than 20" from the enemy.
Fix bayonets: While the human wave is a thing of the past in 44, Soviet tactics tended to emphasize close quarters attacks, with spade, grenade and bayonet. Soviet troops may reroll one failed attack die, if they charge a suppressed enemy squad.
While most Soviet troops in 44 are pretty rugged fellows, if you want to represent quickly rounded up conscripts, add the following rule:
Run away!: A soviet squad fired upon must spend its reaction moving away from the enemy, unless every model fired upon is in cover. Squads within 5" of a platoon commander may ignore this rule.
This rule is mostly appropriate up to Stalingrad. By no means all troops acted this way, so make it an option, to save points.
Finnish infantry (winter war of 39-40 mostly, but they fought the Soviets pretty much through to the end)
Im not up on exact squad details in my head. During the winter war, squads dont nescesarily carry an LMG (IIRC, 2 guns per platoon). For Continuation war, supplies are better (and lots of captured soviet guns are around)
For special concerns and rules:
Stay alive!: While dogged and tenacious, the Finn's also realize that manpower is a very important commodity. Once a Finnish force reaches 40% casualties, every squad will immediately retreat one move directly from the enemy, unless this takes them out of an entrenchment or similar position of cover. No charges may be launched after this point, unless the enemy is suppressed, or the combat occurs entirely within a terrain feature.
Sisu: Roughly meaning "Guts", the Finnish army perfected close terrain commando tactics. A finnish squad may perform a special "shoot and scoot" action, allowing them to fire any SMG's they carry, then move their full move, provided the move takes them directly away from their enemy or into a position of cover. This prevents them from reacting this turn, however.