As I was thinking about the new Lost Brotherhood Strike Force (from the Angels Blade supplement) some more, it struck me that they would synergize very well with an allied Ravenwing force to make a hard-hitting, very mobile, very flexible army.
Here are some synergies I can think of right out the gate:
 Master of the Ravenwing Sammael (as WL) and a DC Chaplain (with Guardian’s Blade Relic) attached to a squad of Death Company (with JPs and a few PFs to taste) from the Lost Brotherhood Strike Force:
So, the way this work is the DC Chaplain/Death Company squad get their free 6″ move before the game begins (Sammael doesn’t get this, but you can “conga line” some models back to keep him in coherency with the battle group). Then, turn 1, you move everyone up 12″, putting you 18″ toward the enemy DZ so far. Next, in the Assault Phase, you use Sammael’s Warlord Trait to add +3 to the unit’s charge range, so a total of 3+ 2D6″… that is a minimum of a 5″ charge range, an “average” charge range of 10″, and a maximum charge range of 15″. Based on all this, combined with the 18″ the battle group has already moved, Sammael, the DC Chaplain, and the Death Company themselves should be able to reliably get a first turn charge on any enemy forces deployed on the edge of their DZ. On the charge, the Death Company would be attacking with 5 x S5 AP- attacks at I5 a piece, all with re-rolls to Hot and to Wound. Sammael and the Chaplain add in some AP2 hitting power at I5, all with re-rolls to Hit, and also provide a little “pre-charge” shooting with their Plasma Cannon and Inferno Pistol, respectively. After this combat phase is resolved (if you didn’t pulverize your opponent in a single turn), you can use Sammael’s Hit and Run to jump back out of combat and “rinse and repeat” the charge on your next turn, thereby taking full advantage of all the bonuses for charging (i.e. re-rolls to Hit/to Wound, Furious Charge, Rage, +1I, etc.). You can also use Sammael to “tank” for the unit after they get out of combat, since he has a re-rollable 3+ Jink save (due to Skilled Rider + “Ravenwing” rule) and EW, which is great for absorbing high strength, low AP shots like Krak Missiles, Lascannons, etc. Finally, Skilled Rider from Sammael also allows the whole unit to ignore Dangerous Terrain tests, which a big boon when moving across the tabletop with Jump Infantry.
 DA Biker Librarian, Ravenwing Black Knights, a Darkshroud, and the Archangel Orbital Intervention Force (3 squads of Assault Terminators) from the Lost Brotherhood Strike Force:
With this one, the Librarian, Black Knights, and Darkshroud all use their Scout ability to get up-field quickly, then move another 12″ + 12″ (Turbo-boost) Turn 1. With the Darkshroud and Skilled Rider giving the RW Black Knights a 2++ cover save (which is re-rollable, thanks to the “Ravenwing” special rule), they are basically invincible to any shooting that does not Ignore Cover, allowing them to survive and then use their Teleporter Homers to bring in the Blood Angel Assault Terminators for a no scatter DS. Once this happens, in the Psychic Phase the Librarian casts Prescience on an Assault Terminator squads for re-rolls to Hit, and then the Archangel OIF Terminators charge that same turn, in all likelihood doing some very serious damage to whatever unit they get stuck in with. The Biker Librarian/Black Knights are also free to charge the same unit or another enemy force, letting you tie up as many as 5 enemy units in a single turn (Librarian charges one, Black Knights another, and each of the three BA Assault Terminator squads each charge a unit). Overall, I think this makes very dangerous and effective close combat battle group combination.
 Ravenwing Support Squadron (with LS Vengeance and 3 x LS Typhoons) and multiple BA Assault Squads (with JPs, 2 x Meltaguns, plus Combi-Melta and Eviscerator on Veteran Sgt) from Lost Brotherhood Strike Force:
In this combination, the Assault Marines use their “free” 6″ move before the game, plus their normal 12″ move to get upfield quickly and engage vehicles with their Melta weapons (and subsequently assault the vehicle as well, if necessary, with the Veteran Sergeant swinging the Eviscerator for 3 x S9 AP2 Armourbane attacks on the charge) while the RW Support Squadron uses it Strafing Run rule to provide 6 x BS5 Krak or Frag Missiles and 18 x BS5 Heavy Bolter shots, plus a S7 AP2 Large Blast, as fire support for the BA Assault Marines. Basically, this battle group put some cheap but dangerous units in the enemy’s face right away (i.e. the BA Assault Marines) while simultaneously providing very solid long-range fire support in the form of the RW Land Speeders. The RW Support Squadron also has the Interceptor rule, so it can provide the invaluable ability to engage enemy units as they arrive from Reserve (something usually only Tau can do) with lots of potent shooting before those units can even shoot, run, or assault (looking at you here, Skyhammer Annihilation Force! 😉 ). Overall, I think combo works well when you are taking a Lost Brotherhood Strike Force as your primary force.