my first idea is golems. These guys would be serious tanks on a battlefield, unfortunately, the cost to create them in the DMG is prohibitive(even on a gold bar standard).

Muster cost: High? The cost to buy a stone golem on the open market is 90,000gp or about 45 Gold Bars!
Maintenance cost: 1/4 GB why? Golems dont need much, except the odd spell to heal their damage, and a few "golem wranglers" who order the golem about in battle.
Defense: 28-30; Golems have Dr 15/Adamantine, and they cant be critically hit. No footsoldier stands a chance at harming it, but then maybe the unit is carrying a few special measures in the rear ranks. A veteran unit should have a very hard time hitting the golem, and an attached hero unit should be able to affect the unit enough to make the rare hit.
Hits: 2-3; the odd chance that they are damaged, you would think it would be from artillery fire or a rare weapon capable of dealing more than 15 damage on a hit. Even so, any damage they do take is going to be small.
Ranged: no
Melee: High Maybe +12 or greater. Even against fortifications, a golem will smash its way through walls to complete it's objective.
Morale:--(nonability) even if the golem wranglers run away or get killed, the golem would still try to complete it's objective. As such it should be considered alot like an undead unit.


"fluff" - I figure a unit of golems is actually a single golem (like a naval unit) with a smattering of lesser unimportant troops whose sole job is to order the golem around. Even though it is unrealistic that a single golem could deal significant damage to a unit of 200 men at arms, you have to consider the way this thing might fight. It would probobly be ordered to charge into the middle of units (trampling/killing several men in the process) and each round its going to kill 2 men at arms. I figure a battle round is alot longer than a D&D round simply because a battle like we're used to seeing would last minutes or longer. That gives a golem ample time to crush and kill 200+ men at arms.