Gotta be WH40k stuff just by the sheer amount of choice in that universe and tremendous reach beyond just a few paltry nerd niches. They have released books, Pen and Paper games, movies (of questionable quality), video games, card games, board games, the classic war games, and a plethora of other stuff. For decades now, to boot.
Personally, after all my favs have already been mentioned, I remember the suits they wore near the end of The Forever War by Haldeman.
"The suit is set up to save as much of your body as possible. If you lose part of an arm or a leg, one of sixteen razor-sharp irises closes around your limb with the force of a hydraulic press, snipping it off neatly and sealing the suit before you can die of explosive decompression. Then "trauma maintenance" cauterizes the stump, replaces lost blood,and fills you full of happy juice and No-shock. So you will either die happy or, if your comrades go on to win the battle, eventually be carried back up to the ship's aid station."
It makes sense to do that if you're too low tech to have self repairing armour and have to fight someone in a suit in vacuum, but that doesn't make it any better. Plus, the idea that the last few fights reverted to medieval Bow and Arrow/Sword/melee engagements inside a pocket dimension and shield bubble was ... memorable. Heh.
Honourable mention to Saber Rider and the Star Sheriffs. Those were more utility suits IIRC, but hey, can't knock armour that comes with a hat. Also I've completely run out of other ideas.