Friends: Top 10 guest stars, ranked

"The One With the Rumor" (Season 8, Episode 9)

Jennifer Aniston's then husband Brad Pitt starred in the season 8 Thanksgiving episode, playing a very different role: a founding member of the "I Hate Rachel" club.

"The One With Rachel's Sister" and "The One Where Chandler Can't Cry" (Season 6, Episodes 13–14)

Reese Witherspoon was utterly perfect as Rachel's even-more-spoiled little sister Jill, who shook up her sib when she briefly dated Ross (David Schwimmer).

Seasons 9–10 (18 episodes)

Pheobe's (Lisa Kudrow) best chance at "normalcy" was marrying geeky pianophile Mike (Paul Rudd), who became a beloved member of the group through 18 episodes.

"The One With Rachel's Other Sister" (Season 9, Episode 8) and "The One Where Rachel's Sister Babysits" (Season 10, Episode 5)

Rachel's other sister was the despicably witless Amy (Christina Applegate), who didn't know her niece's name yet still wanted custody if her parents died.

"The One With Joey's New Brain" (Season 7, Episode 15)

Susan Sarandon played a soap diva (think Susan Lucci) who struck up a romance with Joey (Matt LeBlanc) after he let it slip her character would be killed.

"The One With Rachel's Big Kiss" (Season 7, Episode 20)

Nobody believed that Rachel had actually kissed her former sorority sister, played with hilarious enthusiasm by Winona Ryder.

"The One Where Ross Meets Elizabeth's Dad," "The One Where Paul's the Man," "The One With the Ring" (Season 6, Episodes 21–23)

Action star Bruce Willis won an Emmy for playing the intimidating father of Ross' student girlfriend, as well as Rachel's love interest.

Seasons 2, 3, and 6 (9 episodes)

Tom Selleck — Magnum. P.I. himself — romanced Monica (Courteney Cox) as Dr. Richard Burke, a friend of Monica's father and Chandler's (Matthew Perry) biggest competition.

"The One After the Super Bowl: Part 2" (Season 2, Episode 13)

Julia Roberts got sweet revenge on Chandler as Susie, stealing his clothes and stranding him in the restroom.

"The One With Two Parts: Part 2" (Season 1, Episode 17)

ER hunks George Clooney and Noah Wyle appeared as — this is a stretch — cute doctors who went out with Monica and Rachel.