Anduin makes a reference to The Lion King, with him being Simba and his father, Varian, being Mufasa.
Anduin: My father once said that everywhere the Light touches is our kingdom. But not Deadwind Pass. We don't go there. Explanation Deadwind Pass is the area where Medivh's tower, Karazhan, is. As the name indicates, it is not a pleasant place to be, with undead, demons and other evil beings lurking around.
His phrase when selecting "Change is upon us." was changed in the French version to "Le changement c'est mainenant." (Change is now.) which is a viable translation... and happens to be François Hollande's slogan when he ran for President in 2012.
Sonya: Bul-Kathos, I have never prayed to you before. I have no tongue for it. No one will remember why we fight, or why we die. All that matters is that five stood against five. I ask you, grant me one request. Improve my MMR! If you do not listen, then to Hell with you!
Sonya: Let's see, crush enemies, done. Drive them before me, of course. Hear the lamentations of their women... let's skip that one.
Lots of shout-outs to Hearthstone. Note that Valeera is the Rogue representative there.
Valeera: I'm an excellent Rogue. But I can't perform miracles. Not after that nerf at least... Explanation Miracle Rogue is a famous deck used in Hearthstone and was once nerfed heavily to the point it was unusable. While it has a resurgence recently, it's not as overly powerful as its early incarnation. Valeera:(to Rexxar) Have you ever aimed to somewhere other than the face? Just... curious. Explanation In Hearthstone, going for "the face" is another way to say you directly attack the opponent. The Hunter class, which is represented by Rexxar in Hearthstone, had several decks known as "Face Hunter" decks, where the player mostly ignores the board and just aggressively attacks the opponent directly.
She references the Stock Phrase of "Join the army! See the world! Meet interesting people! And shoot them.". Instead she provides "Join the Scarlet Crusade. Meet interesting and stimulating people. Purify them!"
She may be referring to the The Scarlet Letter when she says "My Scarlet Diviners examined every Scarlet letter of every Scarlet Book in Scarlet Monastery's Scarlet Library... yet none was a Scarlet Thesaurus. So I burnt it down."
A Rogue One reference from Legion also made it to the Nexus:
Yrel: I am one with the Light, and the Light is with me.
Snowfall Alexstrasza, one of her base skin tints, colors her regular attire (and hair) in white, making her look like a certain White Queen.
The Purifier skin for Artanis is clearly based on iconic mechas. note The default tint is similar on colors to the Jaegers, the red tint is akin to Char's Sazabi while the last tint evokes the Unit-01.
Azmodunk and his basketball-themed demons are clearly a reference to Space Jam.
Kerrigan's Cruel Queen of Ghosts skin tint is another reference to Neon Genesis Evangelion (and if you want to go deeper, even the name of the skin is a reference to the theme song; a Cruel Angels Thesis.)
One of Kharazim's base tints makes him look like an older Aang.
His Jade Dragon tints references Avatar in Roku, and Dragon Ball Z.
Space Lord Leoric is a wholesale reference to Darth Vader, complete with numerous iconic Vader voice lines. One of his tints, aptly named "Hunter", appears to be based on the armor of Boba Fett.
A tint for Li-Ming's base skin gives her a distinct orange and red color scheme, which, given her voice actress, might make people think of Azula.
Star Princess/Queen Li-Ming is a reference to Magical Girls, specifically Sailor Moon, with the various color variations referencing the other Sailor Scouts. Out of these, the most obvious one is Thunder Star Princess Li-Ming, colored green and referencing Sailor Jupiter's Shock and Awe powers. Her lore is also a StarWars reference, with Li-Ming basically being Princess Leia.
Stars and Stripes Raynor looks like Captain America. The Agent Stars and Stripes Raynor variation, which is colored black, red and white, might be a reference to the period Steve Rogers went as "The Captain", donning a black, red and white costume; the man who was replacing him as Captain America at the time would later become the "U.S. Agent", an ally hero of his.
One of the tints for his more casual attire, Desert Commander, has a big Reaper skull emblazoned on his black shirt, calling to mind another similarly dressed guy that goes around shooting people with a big gun.
The Garden Terror performs the most famous part of the Thriller dance.
Alarak's Discord Strike (and the key it's assigned to) are both shout-outs to Discord and Q, two roles John de Lancie also played. Discord gets a second shout-out with Alarak's "silly" emoticon, which shows him with Discord's distinctive horn and antler.
Two potential lines from her using her Cleansing Flame ultimate are out of her own card's use in Hearthstone
During his Blizzcon reveal segment, Cho'gall introduces himself with this line from Team Rocket:
Cho: (punched in the face) Prepare for trouble! Gall: (punched in the face) Make it double!
Cho'gall's Q ability is called 'Surging Fist', while it didn't look too familiar with the original, it involves fist, and in Japan, it translates to 'Hadoken'
His Guitar Solo's E ability'snote Regenerates health for 4 seconds icon is a mashup of the Horde's emblem and Prince's Love Symbol. Appropriately, his level 1 Talent note Heals 50% of damage dealt by Basic Attacks while Guitar Solo is active involving this ability is called Guitar Hero.
Due to Gilneas being Victorian era and Gothic Horror inspired it can be dismissed as a coincidence, but talent names like Visceral Attacks and Hunter's Blunderbuss, Greymane often emphasizing that he is "on the Hunt" and his fighting style in general can be seen as a Heroes interpretation of a hunter from Bloodborne.
If Jaina kills an enemy Jaina, she quotes a line from "Let it go".
Jaina: The cold never bothered me anyway!
Aside from the Frozen reference above, her Water Elemental upgrade is called Wintermute.
Junkrat's victory animation is a reference to Fnatic pro player Quackniix's celebratory jumps after winning the Mid-Season Brawl tournament with his team. Junkrat is one of his favorite heroes.
Kel'Thuzad's cat, Mr. Bigglesworth, is also the name of Dr. Evil's cat.
Orphea can be seen as one to Raven with them being similar in so many aspects that she may even qualify as an Expy. Both are young, raven-themedDark Is Not Evil women (with bob cut hair), who firmly oppose their evil father.
A variety of "unlimited" in-game quest talents for heroes are actually capped at 9001 or in other words, just over nine thousand. It's also an Easter Egg because actually attaining so many stacks for any such quests in a real match is virtually impossible.