Buffy the Vampire Slayer

Xander: What'cha got in the basket, little girl?
This is a reference to Buffy's Little Red Riding Hood costume. In some versions of the Little Read Riding Hood fairy tale she meets a wolf in the woods on her way to her grandmothers house and he'll often ask her what she has in her basket. When she gets to her grandmothers house, the wolf has locked her grandmother in the closet (or eaten her, depending on the story version) and dressed up in her clothes to trick Red Riding Hood in an attempt to eat her.

Xander: The man likes his schnapps.
Schnapps is a generic name for a flavorful, usually clear alcoholic beverage made from fermented grain and flavored with various herbs or fruits. Schnapps can come in a variety of flavors including strawberry, peppermint, orange, butterscotch, and many others.

Buffy: If I were Abbott and Costello this would be fairly traumatic.
This is a reference to the comedy duo of Bud Abbott and Lou Costello that had a show together and made several movies in the 1940's and 50's. In many of their movies Abbott and Costello would meet various monsters such as: Frankenstein, The Mummy, and Dr. Jekyll and Mr. Hyde.

Willow (about the camouflaged guys): What are they supposed to be?
Oz: NATO?
NATO is the North Atlantic Treaty Organization, a military alliance established in 1949. Its aim was to safeguard member nations from attack with the end of the Cold War, NATO has increasingly concentrated on extending security and stability throughout Europe, and on peacekeeping efforts in Europe and elsewhere.

Willow: I'm Joan of Arc. I figured we had a lot in common, being almost burned at the stake and having a close relationship with God.
Joan of Arc is a patron saint of France and hero of the Hundred Years War. As a teenager she believed that God spoke to her and urged her to save France from English domination. She lead an army that attacked the English and forced them to retreat from Orleans. The English eventually captured her, tried her for heresy and sorcery, and burned her at the stake. In 1920, she was canonized (made a saint) by the Catholic Church.

Giles: It's alive
As Giles hits the small hanging Frankenstein's monster figure, he says "It's alive." This is an homage to the scene from the classic 1931 film, Frankenstein, in which the Dr. Frankenstein says the same thing when his newly animated monster begins to move.

Willow / Music soundtrack: As Willow begins her attempted will-o-the-wisp spell, the background music quietly changes to the beginning strains of Dukas's "Sorcerer's Apprentice" (or something very much like it). When the will-o-the-wisp first splits in two, the rising strings o' peril from the piece come in just as they would for Mickey's brooms splitting exponentially out of control. This also disproves the earlier notion that Fantasia can't be scary.

Xander: Prepare to have your spines tingled, your gooses bumped by the terrifying ... Fantasia.
Oz: Maybe it's all the terrifying things we've seen, but hippos wearing tutus just don't unnerve me the way they used to.
Fantasia is a Disney movie from 1940 that consists of animated scenes backed by a classical music score. The most famous sequence is probably Mickey Mouse as the sorcerer's apprentice. The movie also contains a scene with hippos in tutus dancing.

Xander: Sensing a disturbance in the force, master?
Reference to the Force, the energy field which binds together all living things, which is featured in the Star Wars series of fantasy/sci-fi films.

Title: Fear, Itself
The title is part of the famous speech given by President Franklin Roosevelt during World War II: "We have nothing to fear but fear, itself."

Xander: Bond. James Bond.
Xander goes dressed as the famous British spy of book and movie James Bond. This is the classic catch phrase of the series.

Oz: Mi casio es su casio.
Oz makes a play on the Spanish phrase "Mi casa es su casa" (My home is your home) along with Casio a brand of electronic equipment.

Frat guy #1: Is there any holiday that's not about getting laid?
Frat guy #2: Arbor Day.
Arbor Day is a little celebrated holiday on the last Friday in April that is supposed to be about planting trees.

Willow: Okay, Brutus. ... Brutus? ... Caesar? ... Betrayal ... trusted friend? ... Back stabby?
Willow explains her own historical reference to Brutus (Marcus Junius Brutus) who was a leader of the conspirators who killed Julius Caesar.