OP, this is a really great question. I do consider all live-action Trek canon. Beyond that, some things that come to mind:
From Trek Lit.
(The novel Ashes of Eden, Lost Era, Astrid Kemal, Commander Quinton Stone, Elias Vaughn, Ethan Locke, Afsarah Eden, Captain Harriman's depiction, Andorian biology/culture, Breen biology/culture, Romulan language/culture, QuchHa/HemQuch Klingons, The Hive, Herans, Thallonians, Danteri, Admirals Cartwright and Dougherty in Section 31, Tomed Incident in Serpents Among the Ruins, Betreka Nebula Incident/Cold War in Art of the Impossible, the Borg incursion in Destiny trilogy (though I'm not that cool with the fate of the SS Columbia in that series), Bodai Shin, Captain Geordi LaForge, Tryla Scott survived "Conspiracy", Va'Kel Shon and the Enterprise-F, Typhon Pact).
From comics
Khan miniseries, Star Trek Countdown, Star Trek: Early Voyages, Star Trek Academy, Klingons: Blood Will Tell, Star Trek: Crew, Captains Logs series,
From video games:
The appearance of the extradimensional Gorn from the last video game, though I'm not cool with the idea of them being outside the galaxy.
Star Trek Borg and Star Trek Klingon and Klingon Academy
From Trek Lit.
(The novel Ashes of Eden, Lost Era, Astrid Kemal, Commander Quinton Stone, Elias Vaughn, Ethan Locke, Afsarah Eden, Captain Harriman's depiction, Andorian biology/culture, Breen biology/culture, Romulan language/culture, QuchHa/HemQuch Klingons, The Hive, Herans, Thallonians, Danteri, Admirals Cartwright and Dougherty in Section 31, Tomed Incident in Serpents Among the Ruins, Betreka Nebula Incident/Cold War in Art of the Impossible, the Borg incursion in Destiny trilogy (though I'm not that cool with the fate of the SS Columbia in that series), Bodai Shin, Captain Geordi LaForge, Tryla Scott survived "Conspiracy", Va'Kel Shon and the Enterprise-F, Typhon Pact).
From comics
Khan miniseries, Star Trek Countdown, Star Trek: Early Voyages, Star Trek Academy, Klingons: Blood Will Tell, Star Trek: Crew, Captains Logs series,
From video games:
The appearance of the extradimensional Gorn from the last video game, though I'm not cool with the idea of them being outside the galaxy.
Star Trek Borg and Star Trek Klingon and Klingon Academy