Sarah’s Sanctuary

Sarah Michelle Gellar was away shooting the Angel episode ‘Sanctuary‘ during the filming of Where the Wild Things Are which is why we see so little of her in that episode.

Alastair Duncan

Alastair Duncan, who played Collins in This Year’s Girl and Who Are You? did voice overs for the video game Star Wars: Jedi Knight - Jedi Academy and played the theatre manager in The Three Stooges. He has also appeared in Maybe It’s Me, Charmed, Providence, Diagnosis Murder, Sabrina, the Teenage Witch, Babylon 5 and Highlander. He played Collins again in the Angel episode ‘Sanctuary‘.

Jeff Ricketts

Jeff Ricketts played Weatherby in This Year’s Girl and Who Are You?. A regular member of the Buffyverse, he has appeared in Angel as Weatherby, and he also played the Spider Monster in Angel’s season four episode Sacrifice. Jeff played Malcolm in Amber Benson’s movie Chance. He also appeared in a couple of episodes of Joss Whedon’s Firefly. He has also appeared in Holes and Clockstoppers.

Kevin Owers

Kevin Owers, who played the Watcher’s Council’s Smith in This Year’s Girl, also appeared in Ballad of the Nightingale and Titanic. He has been in The West Wing and also played Smith in Angel.

Weatherby, Smith and Collins

Weatherby, Smith and Collins were tough members of the Watcher’s Council who helped to abduct Faith (not knowing Buffy was occupying her body) in Who Are You?. They intended to take the Slayer to England to be reprimanded, but she escaped using their van.

Faith’s mind

In the Buffy episode Who Are You? Faith (in Buffy’s body) daydreams that she stabs Willow. A similar scene occurs in the Angel episode ‘Sanctuary‘. When Angel takes Faith back to his apartment she daydreams that she attacks Angel with a knife.

Heading to L.A.

The Buffy episode The Yoko Factor follows on from an episode of Angel called ‘Sanctuary‘, where Buffy turns up in L.A. to find Faith. She’s disgusted to find that Angel is helping her nemesis, despite what she did to Buffy. Angel and Buffy argue, and she leaves. He arrives in Sunnydale in The Yoko Factor to apologise to Buffy. Xander calls Buffy “LA Woman”, referring to her visit to L.A.

So long, Buffy

Sanctuary was the last episode in which Sarah Michelle Gellar appeared in Angel. The character of Buffy appeared in the season five episode The Girl In Question but it was just a blonde head we saw and it not Sarah.
At the end of the episode, Wesley asks Angel is he wants to go after Buffy after their argument and he says yes. This is what leads to Angel appearing in Sunnydale in the Buffy episode The Yoko Factor.

Taciturn Man

Angel and Oz are both referred to as ‘taciturn men’ in Buffy and Angel. Tactiturn means “1. inclined to silence; reserved in speech 2. dour, stern and silent in expression and manner” per the Random House College Dictionary.
In the Buffy episode Enemies, Buffy is wondering how Angel felt about kissing Faith. Willow offers the following advice: “Buffy, I, too, know the love of a taciturn man, and you have to look at their actions.” Here, Willow is referring to both Oz and Angel as taciturn men.
In Angel season one, ‘Sanctuary‘, Angel yells at Buffy for getting angry that he helped Faith. After she leaves, Angel says, “For a taciturn, shadowy guy - I’ve got a big mouth.”

Lost Weekend

Buffy says to Giles in The Dark Age, “I care from you Lost Weekend-ing in your apartment!” The Lost Weekend (1945) is a film about the effects of alcoholism on a man’s life. It was based on a novel of the same name by Charles R. Jackson. The movie won Academy Awards for best picture, best actor (Ray Milland), best director (Billy Wilder) and best screenplay (Billy Wilder and Charles Brackett).
When Faith is channel-surfing in Angel’s apartment in Sanctuary, one of the films seen is The Lost Weekend.

The X Files

The X Files was an influential TV show (1993-2002) following two FBI agents, Fox Mulder and Dana Scully, who investigate the unexplained. It has been mentioned in the Buffyverse on several occasions.
In The Pack, Buffy accuses Giles of trying to “Scully” her (Scully was sceptical about Mulder’s supernatural beliefs).
In Living Conditions, Buffy says about Kathy, “You’re right. Ooh! She’s even affecting my work, now. She’s the Titanic. She’s a crawling black cancer… She’s… other really bad things.” The “crawling black cancer” line is likely a reference to The X-Files. In the show, it’s an alien liquid organism which looks like oil. When someone is first infected by the black substance, it crawls up the body like bugs under the skin.
In Life Serial, the trio of nerds test Buffy using different methods, one of which being a time loop. Warren mentions a similar plot in an X Files episode “where the bank kept exploding”. The episode was called ‘Monday’ and was during season six of the show.
In Gone, Buffy says, “Xander and Anya are working on it. Mulder-ing out what happened.”
In Sanctuary, the following conversation takes place:

Kendrick: “Come on Kate. Everyone knows you’ve gone all Scully. Anytime one of these weird cases crosses anyone’s desk, you’re always there. We used to be friends - what’s going on with you?”
Kate: “Scully’s the sceptic”.
Kendrick: “Huh?”
Kate: “Mulder’s the believer, Scully’s the sceptic.”
Kendrick scratches his head: “…Scully’s the chick, right?”

The X Files returned the favour in it’s season nine episode ‘Daemonicus’ by referencing Buffy with the following dialogue:

Scully: “For the past eight years I was part of a unit known as the X-Files. Some of you may have heard of it.”
Cadet: “Ever slay a vampire?”
Scully: “Sorry to disappoint you, but this is a course in forensic pathology. Hard science. An X-File is a case that has been deemed unsolvable by the Bureau, because such a case cannot be solved it may beg other explanations… a vampire, perhaps.”

Seen at 12.51 minutes:

When Wesley is throwing darts in the bar in Sanctuary, the dartboard is black and white, but when he goes to take the darts out of the board, the dartboard is coloured.