A Look at Imperial Knight Allies
Now that the site is back up and running, I can give my 2 Imperial cents about what I think would make for good allies to fill up the extra points in Imperial Knight armies. I'm going to be looking at 3 armies in particular, Space Marines, Astra Militarum, and Militarum Tempestus, to analyze what they have to offer Imperial Knights. Before getting into that though, we should talk a bit about what Imperial Knights lack. In my experience so far, the two (and probably most obvious) weaknesses of Imperial Knights are lack of boots on the ground and anti-air. When it comes to missing boots on the ground, it is important to remember that your Imperial Knights are all scoring, that said, they're also the primary source of damage for your army and the main thing your opponent will be shooting at. Flyers pose a serious problem to a Knight primary army, as neither of the knights currently available can do a damn thing to a flyer, and against a FMC, you might get a lucky stubber hit and hope to ground them, but that's about it. Now with Tyranid Skyblight in full swing, Necron Air still floating around, and things like Stormravens with flying AP2 missiles and multi-meltas, it's very difficult to totally ignore the skies.
Space Marines
First up on the chopping block are the classic Space Marines. Obviously they don't have many boots on the ground, but they do have some interesting possibilities. If you call them Mantis Warriors, you can take a level 1 Librarian with Divination, plus some scouts to fill up the mandatory requirements. For anti-air the marines have a few options. First of all is the ubiquitous Stormtalon, fairly inexpensive and capable of taking out most AV11 flyers in a single volley, or even doing a few HP to some AV12 flyers. It's not a bad choice for the points, and definitely helps a bit with anti-air, it might not be enough when facing an army that is heavy on air though. In addition to the Stormtalon, there is the Stormraven, which packs a nasty punch, fully loaded with a multi-melta, assault cannon and missiles, it's going to help the fight for air dominance. The Stormraven is also a transport which can keep your probably single scoring marine unit alive and get them into position on the board. If you need something a little cheaper, there's also the Stalker, which is basically going to give you a cheap quadgun, it's not bad and if you're on a budget, spending more points on scoring troops, then this is a great option.
When we factor in Forgeworld, there are 2 units specifically to look at, the Fire Raptor, which is quite expensive, but undeniably an amazing anti-air vehicle, taking it will almost guarantee air superiority, finally, if you're still on a budget and want something that packs a harder punch than the Stalker, you can take Tarantula Batteries with Hyperios Missile Launchers.
There is no shortage of decent AA options for Space Marines, though they are often at a fair premium. Scouts and Marines both offer a solid scoring unit, though unfortunately for their cost, you're going to be coming up a bit short for total number of boots on the ground. Any infantry you take in a Knight Army is going to absorb 100% of the anti-infantry firepower in the enemy army, so you need to have enough bodies to absorb the damage.
Militarum Tempestus
The Militarum Tempesus came out right after the Imperial Knights, and just like the Knights, it's a very small codex. Inside the book you've got moderately priced infantry with a plethora of fast vehicles and AP3 firepower. I've discovered that their infantry make amazing mop-up squads for the Knights, as often times I can't be bothered to fire 2 battle cannon shots at a couple marines left alive out of a squad. When it comes to AA there is one option in the book, the Valkyrie. Unfortunately, GW hasn't gotten the memo that Ordnance is actually a bad rule, so it makes taking the missiles almost pointless, so really it's just up to the lascannon. In summary, don't take Militarum Tempestus if you need Anti-Air. Their infantry though, make top notch scoring troops, as well as effective MEQ killers. The Taurox Prime looks kind of bad on paper, in my experience reserving them is almost mandatory to not give up first blood, but with the twin-linked autocannon and Taurox Battle Cannon, I've been impressed by their firepower fairly regularly, I've even considered giving them the Taurox Missile Launcher with the autocannons, though it's fairly pricy.
Had GW given them the Vendetta (like they said they would in their blog) then I'd actually probably consider Tempestus to be amazing as allies for Imperial Knights. Maybe if they FAQ them in, or maybe when FW comes out with an errata giving them access to some flyers at the very least.
Astra Militarum
The newest book and the now re-named Imperial Guard, the Astra Militarum is pretty much the definition of boots on the ground. Infantry Platoons offer at the very minimum 3 scoring units, on top of that, you can add things like additional infantry squads or conscripts to really get a ton of bodies to pile onto objectives. If you're playing a game with fewer missions, you can also blob up your infantry squads to give up fewer kill points, or to make it harder to shoot the scoring unit off the objective. A unit which I feel should also be mentioned, that doesn't really contribute to boots or anti-air, but is interesting none the less are the Primaris Psykers. These jerks are pretty inexpensive and you can take 3 in an allied detachment, with access to Divination, it simply means that they'll be able to twin-link your reaper chainswords, rapid fire battle cannons and thermal cannons all day long, not bad! For anti-air, there are just a few options in the codex itself. Hydras are the most overt choice for this, though they're not actually my favorite. They're not very expensive, but they do have the problem that they are only really good at shooting skimmers and flyers... That'll work well against Eldar and Dark Eldar, but against armies which are lacking in the skimmer department, after the air targets have been neutralized, they'll struggle to contribute to the game. Out of Fast Attack, we get the more powerful option, the Vendetta Gunship, with it's nasty 3 twin-linked lascannons and it's ability to transport a command squad (or special weapon squad) anywhere on the board. Out of the core codex, that's pretty much it, but what happens when we add FW to the equation? You add a ton, that's what!
First of all, now we're talking about the Avenger, which is a cheap, 150 point flyer with two lascannons and a solid 7x S6 Ap3 shots, a very modest point value on a flyer which can really put the hurt on enemy flyers, vehicles or MEQ infantry. While we're talking about flyers, the other option to really keep in mind is the Vulture, which is generally best armed with a twin-linked gatling punisher cannon... Yeah, that's right, 20 twin-linked S5 shots, which will send AV 10/11 vehicles and flyers to a fiery demise. The other amazing anti-air option that Forgeworld presents are the Sabre Defense Platforms. They're almost the same price as a quadgun, though with a single twin-linked autocannon, but the big advantage is that you can take a ton of them! How many exactly? 3 per squad, up to 5 squads per infantry platoon... so 15 per single infantry platoon. They scout and they're troops, which means they're scoring. Yeah, that's right, a ton of skyfire/interceptor scoring quad guns.
Ultimately, I think that the Astra Militarum are probably the single best choice for allies for Imperial Knights. They provide tons of bodies to hold down objectives, Primaris Psykers to make the most out of your knights, and with FW in the mix, just a smorgasbord of anti-air.