So... all the legions have their own section of the forum, we have a thread on Pre-Heresy Titan Legions, so its probably time the Imperial Army got a thread - particularly given various people seem to have been considering doing an Imperial Army force recently. So, I present to you:

Imperial Army Regiments

Archite Palatines
Commander Lord Commander Thaddeus Fayle
Notable Actions Served with the 28th Expedition Fleet with the Emperor's Children. Involved on Laeran and Istvaan V.
Uniform Red tunic and silver breastplate
Other Info
Source:Fulgrim

Arcturan Dragoons
Commander
Notable Actions Served in the 954th Expedition with the Space Wolves 13th Company
Uniform
Other Info
Source: Tales of Heresy

Byzant Janizars
Commander Lord Commander Hector Varvarus (assasinated on Aureus)
Notable Actions Have a history streaching back to the Age of Strife. Served with the 63rd Expeditionary Fleet with the Luna Wolves. Involved on Davin, 63-19, Murder, Xenobia, Aureus.
Uniform Cream Greatcoats with gold frogging, Chrome Helmets with scarlet cockades
Other Info Possibly one of the 'Old Hundred'
Source: Horus Rising, False Gods, Legion

Calth 2nd Irregulars
Commander
Notable Actions
Uniform Green fatigues and vest, red headbands (like 40K Catachans)
Other Info
Source: Collected Visions

Calth 3rd Infantry
Commander
Notable Actions
Uniform Grey camo uniform, black body armour, grey helmet
Other Info
Source: Collected Visions

Crescent-Sind Sixth Torrent
Commander Lord Wilde
Notable Actions Served with the 670th Expedition Fleet under Lord Commander Teng Namitjira on Nurth
Uniform
Other Info .
Source: Legion

Fasadian 4th Infantry
Commander
Notable Actions
Uniform Sand coloured robes, brown fatigues, white headscarves (similar to Tallarn uniform)
Other Info
Source: Collected Visions

Fasadian 45th Infantry
Commander
Notable Actions
Uniform Sand coloured greatcoat with red cuffs, rebreather, round helm
Other Info
Source: Collected Visions

Fellesian Airbourne
Commander
Notable Actions
Uniform Almost identical to 40K Elysian Droptroops
Other Info Drop infantry. Make use of drop sentinels. Known regiments are the 5th and the 23rd.
Source: Collected Visions

Geno Five-Two Chilead
Commander Uxor Primus Sri Vedt
Notable Actions Fought during the Unification Wars on Terra. During the Great Crusade they fought the Orks on Foechion and the Dragonoid Cadres on Zantium. Served with the 670th Expedition Fleet under Lord Commander Teng Namitjira on Nurth.
Uniform Leather and chain armour bodysuit, yellow silk robes, silver or orange spiked helmets
Other Info Command structure in the regiment is divided between Uxors (female low-level psykers responsible for strategic command) and Hetmans (Company Commanders usually appointed from outside the Regiment). The soldiers of the regiment themselves are gene-bred for strength. The regiment is from Terra and is one of the 'Old Hundred'.
Source:Legion

Jovian Grenadiers
Commander
Notable Actions Fought at the Mondus Gamma Forge Complex during the Martian Rebellion under the command of Camba Diaz of the Imperial Fists
Uniform
Other Info
Source: Mechanicum

Lucifer Blacks
Commander None
Notable Actions The regiment fought during the Age of Strife and the Wars of Unification, but suffered severe casualties that made it unable to continue at regimental strength.
Uniform Black velvet coats and black armour
Other Info Due to the losses it suffered during the Age of Strife and Wars of Unification, regiment was divided up to serve as bodyguards to high ranking Army officers.
Source: Legion

Outremars
Commander The force seconded to the 670th Expedition fleet was commanded by Khedive Ismael Sherard. This comprised only a small portion of the regiment's overall strength however.
Notable Actions Served with the 670th Expedition Fleet under Lord Commander Teng Namitjira on Nurth
Uniform Graphite grey robes
Other Info Soldiers from the Outremers made up almost 7% of the Imperial Army around the time of the Ullanor Crusade. Their Khedives (senior officers) are made up of congenital dwarfs of the same bloodline, and the Grand Khedive is one of the Emperor's foremost advisors. The regiment makes use of weapon servitors.
Source: Legion

Phyrian 2nd Auxillary
Commander
Notable Actions
Uniform Green fatigues and vest, red headbands (like 40K Catachans)
Other Info
Source: Collected Visions

Regnault Thorns
Commander General Gan Karsh
Notable Actions Served with the 670th Expedition Fleet under Lord Commander Teng Namitjira on Nurth
Uniform Spiked Chrome armour
Other Info
Source: Legion

Sallan 11th Infantry
Commander
Notable Actions
Uniform Red greatcoats, silver grey body armour/helmet, brown fatigues
Other Info
Source: Collected Visions

Saturnine Hoplites
Commander
Notable Actions Fought at Pavonis Mons during the Martian Rebellion.
Uniform
Other Info
Source: Mechanicum

Sidthu Barat
Commander
Notable Actions Has a history streaching back to the Age of Strife
Uniform
Other Info Possibly one of the 'Old Hundred'
Source: Legion

Urslavic 12th Infantry
Commander
Notable Actions
Uniform Grey greatcoats with red/brown cuffs, black bearskin hats
Other Info
Source: Collected Visions

Zanzibari Hort
Commander Major General Nitin Dev
Notable Actions Served with the 670th Expedition Fleet under Lord Commander Teng Namitjira on Nurth.
Uniform Red uniform with bronze armour and spiked silver helm
Other Info Make extensive use of armoured vehicles
Source: Legion

As always, any further additions, extra detail and so on are greatfully recieved.

This is an awesome list Red Sorcerer. This could be a great source for IA units. Thanks!