Mengsk Sky Furies, his most niche unit that still peforms well overall, just outshined by blackhammers+rocket troopers.
As you mentioned, Swann Cyclones, they’re not A-move welcome like goliaths but they’re better at dealing with ground targets than them without losing much on anti-air.
Karax Mirages, when they build stargate, they think of carriers, P2 they’re super cheap for what they do, P3 if you really need anti-air because no chrono= 3 years trying to get a carrier out of the stargate.
Vorazun’s Oracles and Centurions, Oracles actually deals a lot of dmg and can disrupt attack waves. As for Centurions, they’re good for Dark Archon comp, even more so when under P2.
Raynor’s Banshees, the banshee calldown is powerfull, but never saw someone actually making them as a unit alongside with bioball, they do struggle vs splash but that’s why there’s the bioball so medics heals them. For splash rockets you’re better off with siege tanks, but they burst beefy targets down faster than the bioball.
Kerrigan’s Broodlords, alternative for ultralisks for a nice frontline for your hydras, works better in infested maps if you’re bored of lurkers or your ally already has ground siege units. Problem is that they can’t enter into omega worms, but that’s about it.
Stetmann’s corruptors, ling+corruptors is a solid comp vs air comps or that reaper/librator terran comp.
Nova’s Banshees, they’re the A-move version of siege tanks if you need to kill swarmy units, although not on infested maps as they’re cd based.
Fenix conservators, I suppose because they require to activate manually instead of automatically doing it. 35% dmg reduction is better than any armor upgrade and works vs spell dmg, I don’t see many playing Fenix, but it’s way rarer seeing someone making use of them.