Something which all the different Imperium factions have lacked, and still lack, is an affordable open-topped transport that provides their infantry with some mobility and protection, but still allows all the embarked models to shoot and/or assault when required. The closest thing to meeting this criteria is the Land Speeder Storm, but while an excellent multi-purpose transport, it is only allowed to transport Space Marine Scouts, so its utility in this role is quite limited for anything besides those Troops.
Enter the Centaur Weapons Carrier, a Forgeworld Astra Militarum vehicle that can be taken as a Fast Attack option in a CAD or Allied detachment (not to mention as a DT for certain DKOK and Armoured Battle Group units). The Centaur has the following stats/rules:
BS3 AV11/11/10 HP2 (Transport, Fast, Open-Topped)
*Heavy Stubber, Searchlight, Smoke Launchers
*Transport: 5 models
*1-3 Centaurs per Squadron, costs 8 MBs per model
On first glance, this vehicle costs the same points as a Land Speeder Storm and seems inferior in almost every way, with less mobility (Fast Vehicle vs Fast Speeder), less firepower (BS3 Heavy Stubber vs BS4 Heavy Bolter and Cerberus Launcher), and roughly the same survivability (AV11 on the front vs the ability to Jink).
So, why even consider taking a Centaur Weapons Carrier? Well, number one, it is not restricted to SM Scouts, so ANY Imperium infantry that can fit into it can load up as passengers (note: unlike Rhinos/Razorbacks, there is no restriction against Bulky models as passengers) and, number two, since you can take up to three Centaurs in a squadron, you can get a lot of them cheaply with even a “bare bones” AM Allied Detachment. On top of this, Centaurs are Fast Vehicles, meaning they can move 12” and then Flat Out another 12” turn 1, setting up an almost guaranteed Turn 2 charge if they are not destroyed (also, almost guaranteed to be in range of short-range shooting like meltas and flamers on turn 2). Combine this with some Psychic support, like say casting Invisibility on the Centaur squadron, and you can rapidly and reliably have up to 15 models in your opponent’s face by Turn 2 of the game.
So, based on all this, what are some tactical applications for the Centaur and allied Imperium units? Here are some ideas that come to mind for each major faction:
 Grey Knights – The Centaur makes an excellent little transport for a 5 man Purifier squad, since not only can the entire unit shoot out of it with SBs/Incinerators/Psycannons, but they can also using Cleansing Flame and assault out of the vehicle all in the same turn, thus maximizing all their different strengths while mitigating their lack of mobility and durability issues.
 Dark Angels – A Centaur makes for an excellent “mobile bunker” for a DA Command Squad with 5 Grav Guns and Relic Banner (making them Relentless). The Centaur can move up-field and have its passengers put out 15 Grav shots at 18” all game long, all the while protecting them from small arms fire and even serving as a LOS blocking vehicle for other DA units (i.e. say some RW Bikers moving up behind the Centaurs).
 Space Wolves – Whether using Centaurs as cheap Bunkers for Long Fangs (all five Heavy Weapons in a Long Fang squad can shoot out, since it is Open-Topped) or as cheap, mobile transport to “Rhino Rush” Blood Claws or close combat oriented Wolf Guard up-field, the Centaur can synergize quite well with a SW force (and again, the Centaur(s) can form an excellent LOS blocking shield for foot slogging Wulfen as they advance toward the enemy as well). Finally, even Lone Wolfs and Wolf Scouts can grab a ride in a Centaur to make them more effective on the table-top, especially in getting into assault.
 Blood Angels – BA Vanguard Vets (whether of the melee or gunslinger loadout) and Death Company without JPs both benefit tremendously from having a mobile assault transport that can move 24” Turn 1 and get them in range to assault the rest of the game. Similarly, basic BA Tac squads (with Heavy Flamers and dual Hand Flamers on the Sgt) and BA Assault Squads (with two Meltaguns and dual Inferno Pistols on the Sgt) get much better when they have a cheap Open-Topped transport to shoot and assault out of.
 Deathwatch – Unlike most factions, Deathwatch can take Terminators in squads of 1-2, which means they can load them into a Centaur (despite each TDA model being Bulky) and move safely up-field, all the while shooting with whatever Heavy Weapons they are packing (i.e. CMLs, Assault Cannons, Heavy Flamers, Melta PFs, etc.). On top of this, they can subsequently charge out of the Centaur later on, maximizing their value as close combatants as well. Aside from Terminators, DW Veterans also benefit tremendously from grabbing a ride in a Centaur, whether using it as a static Bunker for a Stalker Boltgun squad, an Assault Vehicle for a squad loaded up with PWs and Heavy Thunder Hammers, or a mobile firebase for a squad with maxed out Frag Cannons or Infernus Heavy Bolters. Even if you just keep the baseline Bolters/Special Issue Ammo or the DW Shotguns, a 5 man Veteran squad in Centaur is much more durable and mobile than normal for a relatively cheap points investment and suffers no loss in firepower in the process.
 Space Marines – Honor Guard, Command Squads, Devastator Squads, Vanguard Vets, Sternguard Vets, min-sized Tactical and Assault squads, Crusader squads, and even Sniper Scout squads can all take great advantage of a squadron of 1-3 allied Centaur Weapons Carriers. Of all of these, I think Honor Guard are one of the units that truly get the most out of riding in Centaur APC, as it allows them to rapidly move across the battlefield and assault into combat, thereby maximizing their tremendous points-value while mitigating their weakness, namely lack of mobility and no Invulnerable saves. Alternately, a Devastator squad with max Grav Cannons can move into mid-field and set up a massive, 48” “area denial bubble” with their 20 Grav shots fired safely from within the Centaur “bunker” (at least until your opponent takes out the Centaur itself). Finally, the Centaur makes an exceptional transport for a Librarius Conclave, which can use it to move into position to disembark and cast their powers, cast Witchfires from inside the vehicle, and even assault out of the vehicle if you have Iron Arm and Endurance up on the squad!
 Skitarii – Both Rangers and Vanguard can make excellent use of Centaur support, especially since they lack any organic transport of their own, and also because it mitigates their poor durability while simultaneously letting them still use all their firepower to full advantage (especially with their Plasma Calivers, Arc Rifles, etc.).
 Imperial Assassins – Whether it is a Vindicare using a Centaur as shooting bunker or an Eversor/ Callidus/Culexus using it as an “assault taxi” to get the quickly across the board into combat, I think Centaur squadrons can be quite a force multiplier for Imperial Assassins (especially in new detachments, like the Castellans of the Imperium, where you can have up to 6 Assassins on the field at once).
 Sisters of Battle – Dominion squads, Retributor squads, Battle Sisters squads, and Command squads all can benefit from an extra layer of mobility and protection while they employ their ranged attacks to best advantage. Additionally, Centaurs can take Repentia from almost unplayable to very dangerous, since it protects them from enemy firepower and allows them to get into assault reliably, even against units on the other side of the battlefield.
 Inquisition – Henchman War Bands, whether they are close combat oriented (i.e. like DCAs, Crusaders, and Priests) or shooting oriented (i.e. like Acolytes, Joakeros, and Heavy Weapon-toting Servitors), can all benefit from the Open-Topped nature of Centaurs, especially if you take multiple War Bands riding in a squadron of multiple Centaurs (attached Inquisitors can also shoot and/or assault effectively from these vehicles).
 Militarum Tempestus/Astra Militarum – Whether as a transport for Scions/Scion Command Squads or as mobile Bunker for AM Command Squads, Ratlings, and/or Wyrdvane Psykers, there are lots of applications for the Centaur with a MT/AM list proper, especially if you flood the battlefield with them (i.e. up to 9 Centaurs if you take three squadrons of them in CAD Fast Attack slots). In particular, I think Scion Command Squads with four Hotshot Volleyguns and AM Command Squads with four Special Weapons are excellent candidates for grabbing a ride in Centaur APCs.
As you can see, there are numerous options for utilizing Centaur Weapons Carriers with Imperium allies, and I did not even touch on using them as a “Hero Hammer APC” to ferry around 1-5 Independent Characters for shooting, Witchfires, and/or Assault (i.e. imagine, say, an AM Priest and four Wolf Guard Battle Leaders with Runic Armor and TH/Wolf Claws all assaulting out of a single Centaur). Bottom line, while this is a little known Forgeworld vehicle, I think it could be a tremendous boost to the competitive lists of most Imperium armies out there.