These nodes contain spoilers! (Even this list itself may contain minor spoilers)

Please /msg me with additions and corrections.

Books

• Harry Potter and the Philosopher's Stone / Harry Potter and the Sorcerer's Stone
• Harry Potter and the Chamber of Secrets
• Harry Potter and the Prisoner of Azkaban
• Harry Potter and the Goblet of Fire
• Harry Potter and the Order of the Phoenix
• Harry Potter and the Half-Blood Prince
• Harry Potter and the Deathly Hallows
• Quidditch Through the Ages
• Fantastic Beasts and Where to Find Them

Characters

Muggles

• Petunia Dursley
• Vernon Dursley
• Dudley Dursley
• Piers Polkiss
• Mark Evans

Gryffindor

• Godric Gryffindor
• Harry Potter
• Hermione Granger (Emma Watson)
• Charlie Weasley
• Fred Weasley
• Ginny Weasley
• Percy Weasley
• Ron Weasley
• Oliver Wood (Sean Biggerstaff)
• Albus Dumbledore (Richard Harris)
• Sirius Black (Gary Oldman)
• Rubeus Hagrid (Robbie Coltrane)
• Lee Jordan
• Neville Longbottom
• Minerva McGonagall (Maggie Smith)
• Nearly Headless Nick (John Cleese)
• Peter Pettigrew
• Remus Lupin

Hufflepuff

• Helga Hufflepuff
• Cedric Diggory

Ravenclaw

• Rowena Ravenclaw
• Filius Flitwick (Warwick Davis)
• Cho Chang
• Penelope Clearwater
• Luna Lovegood

Slytherin

• Salazar Slytherin
• Severus Snape (Alan Rickman)
• Draco Malfoy
• Lord Voldemort (Ralph Fiennes)
• Tom Riddle
• Bellatrix Lestrange
• Horace Slughorn

Other Characters

• (See Harry Potter and the Philosopher's Stone for a full list of all characters in Book 1)
• Nicolas Flamel
• Gilderoy Lockhart (Kenneth Branagh)
• Griphook (Warwick Davis)
• Moaning Myrtle
• Professor Quirrell
• Rita Skeeter (Miranda Richardson)
• Madam Pomfrey
• Fleur Delacour
• Norbert
• Lucius Malfoy
• Narcissa Malfoy
• Aragog
• Argus Filch
• Mrs. Norris
• Dobby
• Fawkes
• Nymphadora Tonks
• Crookshanks

Other

• J.K. Rowling
• Hogwarts School of Witchcraft and Wizardry
• Harry Potter Interactive DVD Game: Hogwarts Challenge
• Draco Dormiens Nunquam Titillandus
• The Sorting Hat
• Muggle Studies
• Beauxbatons Academy of Magic
• Durmstrang Institute
• Harry Potter Spells
• Expelliarmus
• Priori Incantatem
• Harry Potter Trading Card Game
• Whomping Willow
• Triwizard Tournament
• Quidditch
• Bludger
• Golden Snitch
• Floo Powder
• Blast-Ended Skrewt
• The Mirror of Erised
• Veela
• Basilisk
• Dementors
• Inferi
• Norwegian Ridgeback
• Animagus
• Mudblood
• Parseltongue
• Metamorphmagus
• Marauder's Map
• Auror
• Horcrux
• knickerbocker glory
• Every Flavor Beans
• Chocolate Frogs
• Diagon Alley
• Knockturn Alley
• Ministry of Magic
• Gringotts
• The Knight Bus
• Sorcerer's Stone
• Comet Two Sixty
• Nimbus Two Thousand
• Nimbus Two Thousand and One
• Firebolt
• Invisibility Cloak
• Remembrall
• Daily Prophet
• Unforgivable Curses (Avada Kedavra, Imperius/Imperius Curse, Cruciatus)
• Character names in Harry Potter
• Muggles For Harry Potter
• Harry Potter and Leopard-Walk-Up-To-Dragon
• Tanya Grotter
• Harry Potter Nimbus 2000 Broom
• Butterbeer

Essays, Rants, Jokes, and Riff-raff

• Harry Potter and the Treehouse of Horror
• The Secret Connections Between Harry Potter and Star Wars
• Harry Potter or Sex?
• Harry Potter is a *ix hacker!
• Schools ban Harry Potter
• Late Night with Harry Potter
• Harry Potter and the Nation of Dweebs
• Harry Potter and the Right to Bear Arms
• The epistemology of Harry Potter

Thanks to Morgan, Queequeg, Cid Highwind, ratbastid, Rancid_Pickle, urthpaw, and a plethora of others.