Land Speeder Vengeance
The Dark Angels are known for hogging several technological marvels for themselves and their Unforgiven successors that for some reason never quite reached the Adeptus Mechanicus like most such discoveries are meant to....because the Angels are not good at sharing shit.
The origins of the Vengeance can be traced back to the 36th Millennium (no specifications if it was early, middle or late). Back then the Dark Angels stumbled upon an STC belonging to a bigger, bulkier Land Speeder with superior lift-engines that could allow the machine to be outfitted with weapons normal Speeders wouldn't be capable of lifting. The Dark Angels had, for a long time, an ancient weapon in the armory of The Rock. An ancient Plasma Storm Battery that was collecting several millenia worth of dust which they didn't know what to do with...until they found the aforementioned Speeder STC. They mounted the plasma weapons on it and so the Vengeance was born. Since its creation it has served the Ravenwing as a very much needed mobile weapon platform.
The Speeder itself
To briefly describe the Land Speeder Vengeance, if a normal land speeder could be compared to an assault bike, the Vengeance is a flying tank. It is a larger version of the Land Speeder with more dakka that serves as a quick response heavy weapons platform. Its speed can let it fly to a trouble spot quickly and its Plasma Storm Battery can make melted smears of the enemy in an equal amount of time. The downside: it's a 140 point Land Speeder. 50 for the Speeder, 90 for the plasma, and no protection on your AV10 flying kill-machine beyond a basic jink. Deploy it wisely. It'll also glance itself to death in a few turns due to the fact that
the Imperium everyone forgot how to install cooling systems on vehicles somewhere around 6th edition. Which is weird both because the weapon was made back during the Great Crusade when plasma weapons worked great, and because the Dark Angels use properly cooling plasma weapons otherwise.
Alternatively, you can really hurt someone's feelings by including this in a Support Squadron and having Interceptor and Supporting Fire on a chassis that
can forgoskips normal shooting (because it nuked some late arrivals a minute ago) in order to make your opponent forget you're playing MEQ and not the pointy-eared bastards.
Hop forward to 8th edition and... it's a lot better. First off, it has a good amount of wounds but not enough to qualify for a degrading statline, which is awesome. The Plasma Storm Battery is one of the few Plasma weapons that is Damage 2/3 depending on if you supercharge or not and has pretty large fire output which is boosted further with the help of Weapons Of The Dark Age and an Assault Cannon on top of that. This is the Dark Angel's Plasma fetish going too far. But they don't care. Still looks awesome too...
Darkshroud Land Speeder Vengeance
The Dark Angels also like to kit their Vengeances out sometimes with a holy relic instead of a deadly super weapon. This is not just for show and tell however; the relic, called the stone guardian, is a potent arcane creation capable of creating a barrier known as the 'Shroud of Angels' which cloaks the Vengeance in an aura of darkness that can repel even the worst of enemy fire. This does come at a two-fold cost, however. First off, the statues are soaked in Warp energy, and the stormclouds are caused by said Warp energy. Second, you're dropping the most powerful weapon on the vehicle, so it is a bit of a toss up between more protection for your army or more heavy firepower. Decisions, decisions....
Actually, it's usually a pretty easy one: are you running more Ravenwing than everything else? If yes, take the Darkshroud. You'll thank us later when your basic bikers get a 3+ jink save and your Black Knights get a 2+. Otherwise, feel free to splurge for that Vengeance and go to town on anyone bold and foolish enough to run TEQs against you.
Taking Black Knights? Make room for this. No, really. Between Ravenwing's jinking and the Darkshroud screwing with opponents' overwatch, your Black Knights will give your opponent some bad choices.
In 8th edition... goodbye 2+ re-rollable jink and hello -1 to hit bubble. That sounds bad at first until you realise... 1) Dumping this thing next to a unit helps it against a lot of small-arms fire power, 2) The jink was nice but your weapons consisted of a Heavy Bolter/Assault Cannon hitting on 6s because you jinked (also did nothing against Ignores Cover stuff) and 3) Never underestimate a -1 To Hit bubble, especially if you like overcharging plasma weapons. Or you will be sorry.