|Its just an iconic thing|
Ok, now follow me here because we're going a bit into the rabbit hole. Many IG players, myself included, got into this faction because of a love of armored warfare. While 7th edition has rebalanced vehicles a bit, many armies are still flooded with infantry based deathstars while IG seems restricted to Pask and fearless conscript blobs if we want a faction specific 'deathstar.' Well, the Steel Host is our answer by making it our primary detachment.
Start with a Steel Host (yes, formations are both Battleforged and can be your primary.) Add in the Russ and Hydras to taste. At lower points this can even be your entire army since five Russ and a Hydra (the minimum) are a fair bit of points. If you have more room, consider adding other formations (a few Space Wolf ones are cheapish and nice *void claws*cough*void claws*) and detachments such as an allied detachment or assassins.
This allows the IG player to field something similar to an armored formation without having to have all of those pesky infantry mucking about and the formation bonus (12" bubble of Preferred Enemy from the Command Tank) is a great equalizer, especially for those tankers sick and tired of rolling ones to wound with their demolisher or battle cannons.
Also, don't forget that the formation's required Tank Commander can be upgraded to Knight-Commander Pask if that is what you're wanting.
An example list for 1850 points.
Steel Host Formation:
Tank Commander Executioner - Hull Lascannon and Sponson Plasma Cannons
Leman Russ Executioner - Hull/Sponson Heavy Bolters
Leman Russ Demolisher x2 - Hull Heavy Bolters
Leman Russ Exterminator x2 - Hull/Sponson Heavy Bolters and a Heavy Stubber
Leman Russ Vanquisher - Hull Lascannon
Hydra Flak Tank x2
Officio Assassinorum Detachment:
Imperial Knight Detachment:
Cover and fire. The tanks pick their best targets and cut loose. Demolishers will take the forward position of a circle based on the commander, granting their to wound rolls the PE bonus. The Vanquisher will be in the back, taking a sniper roll and hoping that PE helps with accuracy. Exterminators pop light armor and make sure hordes are shredded. Hydras go where they're needed but might be in reserves to get the drop on some flyers.
The Knight can add its firepower but also acts as a counter charge unit, moving where the enemy might intercept or deep strike into your armored line and hitting them back until their a red pulpy mess. If the enemy is a conventional army, the Knight will advance and delay the enemy so that your tanks can get more turns of unmolested firing away.
The Callidus Assassin serves to hurt and delay...it will probably die doing so. It can alpha strike a unit with its flamer, force the enemy to waste a turn and a unit or two dealing with it, and helps to delay their reserves and increase your chances of first turn. It can also sit on an objective you need that is in the enemies deployment area if you're playing maelstrom.
This list captures the feel of both 7th edition and Armored Company in my mind. The tanks are the clear focus of the list but I've added allies and detachments to assist them in their battles.