Games Workshop has started taking pre-orders for some new Cult of Mechanicus units over in their webshop, as well as bundling some of the products together. And, since having the rules for the units is generally a good idea, they've got the new codex up for pre-order as well. As per usual, they've got the regular version as well as a special deluxe edition (limited to 900 worldwide) that you can get, if you're really into the new models and book.
The Cult of Mechanicus... are like the Empire-sanctioned version of the Borg when you read about them. They take biological forms and remove all that "humanity" nonsense and instead replace it with cold, calculating, robot-stuff. They graft on all sorts of weapon mounts and tool bits and will trade out things like "legs" with tank treads. They have a fanatical devotion to machinery and will simply scour worlds clean, looking for resources in order to fuel their foundries and forges. So yeah... Borg.
Now, I'm sure there's a bunch of Trekkies out there that'll tell me how wrong I am in that analogy. And that's fine. I just call it as I see it.
Anyway, along with the codex (both varieties) and a new transfer sheet, there's some new models to check out. There's the box set that lets you either create the Corpuscarii or Fulgurite Electro-Priests, as well as the pack that gives you the "guy in charge" in the form of the Adeptus Mechanicus Tech-Priest Dominus.