Fred and Gunn kiss for the first time in the episode Waiting in the Wings.

In Provider, Lorne says of the Nahdrah’s ship, “Jules Verne meets Leona Helmsley.” Billionaire Leona Helmsley married a real estate tycoon who, under her influence, began a program of conversion of apartment buildings to condominiums. In the 1980s she became infamous for two things – being a tyrannical “boss …

Lorne says of the Nahdrah’s ship in Provider, “Jules Verne meets Leona Helmsley.” Author Jules Verne (1828-1905) is best known for his novels relating to travel, including 20,000 Leagues Under the Sea and Around the World in Eighty Days.

In Birthday, Cordelia checks to see if she has any demon deformities, including horns and a tail. These are also the first things that Buffy checked herself for in the Buffy episode Earshot when she gained an aspect of a demon.

Lilah references Shakespeare’s Macbeth in Dad when she says, “Dusted during childbirth is more like it. According to our sources she staked herself, leaving the baby alive and kicking but never actually born. MacDuff was from his mother’s womb untimely ripped.”
In Shakespeare’s play the three witches’ prophecy read that “…none …

Lorne moves into the Hyperion hotel in Dad, after the destruction of Caritas in the previous episode Lullaby.

In Dad, written on their list of possible threats to Angel’s baby, Connor, is The Scourge - the Nazi-like pure-blood demons from the first season episode Hero.

In Lullaby, Lilah says, “Harvey? It’s Lilah. I got a job for you… Angel Investigations. Yeah, full cleaner service.” This could be a reference to two ‘cleaner’ characters played by Harvey Keitel in the movies Pulp Fiction and Point of No Return.

In Quickening, Cordelia says, “Nothing a couple of Band-Aids and a pint of Heath Bar Crunch can’t fix” referring to the popular brand of US bandages and one of the many flavours of Ben & Jerry’s ice cream.

In Welcome to the Hellmouth, Willow reveals to Buffy that she and Xander broke up after he stole her Barbie, referring to the bosomy Mattel doll. In Offspring, Lorne says, “This is way beyond my ken - and my Barbie, and all my action figures.”

In Offspring, Fred tells Angel about a Pylean word which reminds her of his and Cordelia’s relationship:

Fred: “Kyrumption. It’s the one nice word I remember from the Pylean hell dimension.”
Angel: “What’s it mean?”
Fred: “It’s when two great heroes meet on the field of battle and recognize their mutual fate. …

When Billy goes to his cousin’s apartment in Billy, we hear “Clint Eastwood” by The Gorillaz.

In Fredless, Fred’s father and Angel have the following conversation:

Roger: “Now, Spiro Agnew, I know he was…”
Angel: “A Grathnar demon! You knew that? I thought I was the only one that knew that!”
Roger: “What else would he be, but a demon?”

Spiro Agnew was the thirty-ninth Vice President of the United …

According to Jane Espenson’s DVD commentary for the episode Superstar, Buffy is supposed to say “I’m just kidding!” over the credits at the end of the episode. Espenson probably wrote the line in the script but it was cut later and she didn’t realize it.

In Fredless, Roger Burkle and Angel have the following dialogue:

Roger: “Well, I tell ya, I hadn’t seen a stroke like that since Nicklaus took on Gary Player in the ‘63…”
Angel and Roger in unison: “Bob Hope Desert Classic.”

They’re talking about a PGA Tour golf tournament which is played each January …