Warning: The theme of this army is based on the Nazi Regime. NOTE: This is not my personal belief, it's simply a theme my friend and I came up with when coming up with
IG strats. So please, do not flame me. You don't have to view it.
My friend and I were coming up with a way to make
IG as theoretically broken as possible in an offensive aspect. The main theme is based around Commissar Yarrick(his title is Russian, yes, but disregard that for now), Grey Knights, Usarkar Creed, and Priests. As well as some of the tactics that Hitler used in WW2, such as chemical warfare and other scientific weapons...
Also: Creed can be replaced with Straken
But basically, the main unit is... Yarrick, full squad of Grey Knights(no spec weps), a Priest w/ or w/o Evisc.(maybe two, if rules will permit) And this unit is the primary flanking unit(not to be confused with outflanking) And Creed is there to give them Furious Charge, and order other units whenever needed. If using Straken, he and his
CCS will follow up closely behind Yarrick and the GKM to provide both Furious Charge AND Counter-Charge (which will give
FC even when assaultED, if I read the rules correctly) and he can even help assist in the actual assault(Not to mention he can crack
LR's by himself). But I don't know if this would keep the fluff intact as much as Creed would. And to add on to that, add in a Priest with or without an Eviscerator, to add that extra ablative wound and a couple extra punches. And another side note: If you take Creed, give a 6" scout move to this unit.
As for standard troops, pretty much just naked Veteran squads, suited out with Shotguns and Carapace(maybe, doctrines are optional) and send them in Valkyries, or Vendettas(whichever way works) and they will be sent out to the front lines first... bringing a whole new definition to Shotgun Opera, and they will 'weaken' the opponent with their Assault 2 shots, and can even distract the enemy squads through assaulting. This will give time for your primary unit(the Krieg of the Blitz) to get up the field semi-safely and into assault.
And for Fast Attack, you will obviously need 2-4 Valkyries/Vendettas, but for fluff's sake I thought some Banewolfs and Hellhounds would fit in nicely.

Maybe a tank squadron or two of these. The order is really up to, seeing as they're the same point cost. And they're purpose is pretty much self explanatory.. Nazis were well known for using both chem-gases and incendiaries, so it works for both of this tanks.
Finally, Heavy Support. Really, the tank load out is up to you, but I chose Executioners. Plasma seems like a fitting choice of tank artillery, seeing as Nazi Germany actually researched and engineered similar technologies.
Now, of course if you were to put this as a list, it would be very expensive.. But I feel it would be very effective.
For those of you wondering, here are the roles for each unit: (I don't know the exact chain of command that hitler used, so please forgive me if it's not 100% exact)
-Creed: General in command, ordering the entire army and keeping everything in check.
(Alt.)-Straken: General in the fray, ordering those immediately around him and keeping the army on the offensive lines.
-Yarrick: Commander of the assault, and assault's specialist(I dunno how exactly to put it)
-Priest(s): Masters of torture, taken from the camps and placed on the battlefield
-Grey Knights: Technically are already considered the "Cleansers of the Unpure," so you can probably guess from that(Could be considered as the
SS)
-Veterans: Typical nazi soldiers, disctracting the enemy at the front lines
-Valkyries/Vendettas: (I recommend using Vend's, for
AT purposes) the Zeppelin's of WW2 converted, pretty much.
-Hellhounds & Banewolfs: Mobile gas chambers?
-Executioner: King Lion tanks, that exemplify Germany's scientific research in weaponry
Once again, please don't flame