Dark Angels
First Space Marine Legion to be formed by the Emprah.
Also, totally gay. See "Lionel Johnson" on TOW.
For some reason, they used to have really cool black armor, back in the days when everyone had Corvus pattern (beakies) and 40K wasn't all GRIMDARK all the time. Now they have some weird, like, dark moss green or some shit, I dunno. Also feature bone-white Terminators (Deathwing Company), like from Space Hulk those were Blood Angels my dear sir, making Deathwing the coolest bunch of Terminators around.
They also have the Ravenwing, an entirely Bike and Landspeeder company whose Master possesses one of the last jetbikes in the Imperium. As if that wasn't enough, it has a fuckass huge gun bolted on.