Perry also dated Julia Roberts who had a cameo on the show.
Off the top of my head, Courtney Cox’s husband at the time, David Arquette, played Ursula’s stalker; Aniston’s at the time husband Brad Pitt played Will, the co-founder of the “I Hate Rachel Green Club”; Joshua was Aniston’s fiancé and then ex-fiancé while on the show; and Joshua’s dad was played by Matthew Perry’s dad.
Four actors that were referenced or alluded to also appeared on the show: Winona Ryder was mentioned when the friends used her name to get a restaurant reservation and was on either Chandler or Ross’ celebrity freebie list. She then appeared as Rachel’s sorority sister who still passionately loved Rachel.
The boys love Die Hard and then Bruce Willis came on the show as Paul (Elizabeth’s dad). Apparently Willis did this role for free as a bet payment to Matthew Perry (Ocean’s cast mate— Edit: The whole nine yards*)
Susan Sarandon was mentioned in the freebie list (“she’s too political; would probably make you donate cans of food first.”). She was Jessica before her brain was put into Dr. Drake Ramoray’s body.
Jessica Rabbit was on Chandler’s freebie list and the voice actress for Jessica Rabbit played Charles, Chandler’s dad.
Any more cameos of people that were mentioned in-universe or actors that had relationships with the main cast?
Edit: u/CornishAndPasty reminded me that Aniston’s father is a long-time actor in Days of Our Lives (The soap opera Joey acts in)
Edit 2: the comments are full of lots of great ones I missed! There are too many to easily add up here.
Edit 3: another two I thought of:
Ursula (phoebe’s twin) works at the same café that she works at in “Mad About You” putting those two shows in the same universe. Two guests from that show come in and mistake Phoebe for Ursula in Central Perk.
The Russian dry cleaner (Ukrainian actor Ilia Volok) says he doesn’t like Harrison Ford movies. He was a villain in both Air Force one (which Joey mentions as a good film) and Indian Jones KotCS
