My 3 Class Ideas:
Supplier
There should be very limited ammo, so that players would make their decisions carefully. Teammates who come up to the supplier instantly get their ammo replenished. The supplier, however, has a limited amount of ammo that he has to replenish himself by picking up dropped weapons or finding an ammo stash(these could be placed in certain areas in the maps). But what does he have to defend himself, you ask? The supplier carries an American WWII machine gun that he can only use by propping it on something. He is required to shoot in small, but powerful bursts, since overheating the weapon is very easy. This leaves him defenseless at times. But right clicking makes him take out his brass knuckles and punch. Middle clicking props his weapon. 2 suppliers per team.
Boss
The boss increases the power of the teammates around him. He uses a M3 submachine gun that is slightly weak but can slow down his enemies. Right clicking makes him put his weapon away and cup his hands over his mouth, yelling at his teammates, increasing their power and abilities. He has to wait for his command charge to get full so that he can increase the ammo, firepower, health, and speed of his teammates for a certain amount of time. He has to choose only ONE of those, though. Yes, he can yell while running, but it makes him defenseless for 2-4 seconds. There can only be one boss per team.
Medicine Man
The medicine man can heal his nearby teammates by taking out a needle and pricking them. Him and the teammate he's healing have to stand still, because the healing process acts like the Infiltrator's backstab. The weapon he uses is the U.S Rifle M1903 Springfield. It fires faster than the revolver but is not as powerful. It makes up in accuracy, however, and can reach enemies reasonably far, but not as far as the sniper. Think half of how far you can see with a sniper rifle. There is no limit on how many medicine men there can be.