In this post I'm going to go over the formations for the IG, BA and Marines. I'm not going to go in to all of them in detail, just the ones that I like and think will be useful to me. I'll probably miss a few along the way, I'm not that up to date on them all and haven't bothered with all the supplements and campaigns. Any way, I'll start with the IG ones as there aren't that many;
The Steel Host, a armoured formation consisting of a tank command squadron leading a couple of LR squadrons with a Hydra for some AA. Useful if you have lots of tanks, but I don't have enough to field this
Rampart Detachment, a command squad plus a couple of bullgryn units. Again, it could be useful but I don't own the bullgryns.
The BA formations There are quite a few out there, especially with the Shield of Baal, but these are the ones I'm interested in;
The Angles Wrath, a Vanguard Veteran unit and 2 Assault squads, the advantaged is a single reserve roll and the assault squads don't scatter if they come in with the vets. The bonus of causing hits to enemy models close by is also good.
The Flesh Tearers Vanguard Strike Force also looks good, 3 Tactical squads, 1 Assault squad, 1 Vanguard vets and 1 Furioso dread. A good solid formation, with the charge and initiative bonus' also being good.
The Defenders of Cathedrum is the last formation I like the look of. With 1 Terminator squad, 1 DC squad, 2 Tactical squads, 1 Assault squad and a Furioso dread, its similar to the Vanguard Strike Force, but the extra rules will make this unit difficult to shift.
I'm not really interested in most of the other formations because they tend to include either a Stormraven or a Stormtalon, neither of which I have or wish to acquire at this time.
The standard SM formations also tend to contain either of the flyers, mostly the Stormwing and Saint Tylus battle force. The Strike Force Ultra also looks good, but I have not intention of fielding that many Termies. The one formation that does look good is the Reclusiam command squad, ok so its a dataslate rather than a formation, but I still like the look of it and it contains everything that I would field anyway.