In the Moon Cliffs in Khrysalis, there's a quest where some type of storage area was being burned down by some fire elementals, who say, "Burn, baby burn! Honeymill inferno! Burn, baby burn! Burn it all down!", a pretty obvious reference to to the song Disco Inferno by The Trammps.
I've checked this entire thread and I've seen someone mention it but not in detail.
In The Vault of Ice, the three defenders of the fang are based of The Weird Sisters, (or The Three Witches) in Shakespeare's play, Macbeth. Just read what they say.
Play Quote: Fair is foul, and foul is fair Hover through the fog and filthy air. Protector of the Fang: "Fair is foul, and foul is fair. Try and take this Fang if you so dare..."
Play Quote: (couldn't find the quote in the book that this was referencing. if anyone would like to post it for me, that would be greatly appreciated.) Defender of the Fang: "'Tis the Fang you've come to claim as your own? Tamper with me, little Wizard and I'll turn you to stone!"
Play Quote: Show his eyes and grieve his heart. Come like shadows; so depart! Guardian of the Fang: "Show your eyes, and grieve with your heart. Come to the shadows, and prepare to depart!"
In the Kondhar desert in Chrysalis, there are a couple white mice (cannibals apparently) barbarians- Evandyr Halfear, and another one that shows up during a sparring match called Tyson Uppercut. When I caught on to who they were referring to I almost snorgged my milk out of my nose. Hilarious!
All of Avalon is a reference to movies that have settings taking place in the high stage medieval setting. Most notably is King 'Artur'orious, Sir Rob Bravely, and the minstrel, which all reference Monty Python and the Holy Grail.
Adding on to my other post I found a cool easter egg in Zafaria, so in the zoo in Stone Town, there is an elephant named Jorton Whoghard. That is a reference to the book Horton Hears a Who. To make it even more funny if you complete the side quest he gives you he says something referencing "a person is a person no matter how small" also just saying if you are thinking of completing this quest it has a boss, and 2 defeat and collects.
For star wars easter eggs in wizard101, this is Not really an easter egg, but you can be named luke skywalker. Particularly, kingsisle also officially noted the luke skywalker name on an blog, with an picture of an...cosplay I guess? They also noted it was the name used for the first wizard ever created. There's also the badge "one in an million", potentially referencing han's line "Great shot kid, that's one in an million!" Though, I do assume the term was an generally used term decades prior to star wars and wizard101.
Don't know if this is already posted, but: The final quest chain for Empyrea Part I revolves around Mellori being "only mostly dead", a reference to the film The Princess Bride. It comes with the Badge "Only Mostly Done", which I only mostly want.