As well as datasheets for the plastic Horus Heresy SM units first released in Betrayal at Calth, which can now be included in SM formations, there are a host of formation datasheets too. Most of these first appeared in the Kauyon expansion, but it also includes the feared Skyhammer Annihilation Force. Although most of these formations show either White Scars or Raven Guard, which featured heavily in Kauyon, they are open to all SM chapters too.
Speartip Strike -£50
Stormbringer Squadron -£53
Shadowstrike Kill Team - £56
Raptor Wing - £75
Blade wing Assault Brotherhood - £93
Hunting Force -£95
Pinion Battle Demi-Company -£105
Raven hawk Assault Group - £108
Shadow Force - £109 - unless you can find the Solaq box still
Skyhammer Orbital Force -£136
Skyhammer Annihilation Force - £151
Stormlance Battle Demi-Company -£200
Each of these formations performs differently on the battlefield and depend on you knowing how to use particular units and combinations of rules and tactics. Their performance may not be optimal at the minimum levels. For example, the Pinion Demi-Company works best with more than just one Scout squad to give another unit the Outflank rule.
I have tried the Skyhammer Annihilation Force a few times. Read my review of my first game here.
Up to now, I have only spoken about Space Marines of any chapter in the generic or 'vanilla' codex. Every codex chapter - so not Blood Angels, Space Wolves, Dark Angels, Grey Knights or the new Deathwatch - can use the same formations and Gladius Strike Force detachment in the main codex. Black Templars have the restriction that their Crusader squads can't be used in the Gladius, but they still have Tactical Squads for this.
Angels of Death has one detachment usable by all SM players, which is the Anvil Strike Force. This is one for the petrol heads! Both Core choices in the detachment are based on tanks and are the Land Raider Spearhead and the Armoured Task Force formations from the codex. The latter is the slightly cheaper option if you take the tanks in minimum-sized units of one. I have used this formation once with the help of a few proxies, when it beat a Tau force, although my opponent did not have any of the really scary stuff, as he only took one Riptide. There was a lot of wrecked armour at the end of the game! As with the other formations, the tank units get better rules with units of three, so be prepared to buy more tanks later on.
The detachments in Angels of Death all use different core and auxiliary choices chosen from either the codex or the supplement, however the rest of the detachments are restricted to one set of chapter tactics. This means that you either need to use one of the main, 'first-founding' chapters and have painted models to match, or you declare models with your own colour scheme to be a successor chapter for whichever rules you choose. Many players in a friendly environment are fine with you changing your chapter tactics between games, but if your models look like one named chapter, you will have to use their tactics in more formal games or tournaments.
There are Decurion-style chapter-specific detachments in Angels of Death for White Scars, Imperial Fists, Iron Hands, Salamanders and Raven Guard. All of these use core choices starting at around the £100 mark, to which you need to add at least one auxiliary choice from about £50 upwards. Each detachment reflects the chapter's character and fighting style, so Imperial Fists get amazingly accurate bolters, Salamanders get stronger flamers etc.
Again, which one you choose can only really be determined based on your preferred chapter and models, so make sure you try out a few different types of unit before planning any greater expense. My ultimate plan is still to make my own chapter to ally with my Howling Griffons and Dark Angels, so I can try out some of these detachments.