Dermot Mulroney
Dermot Mulroney is probably one of those faces you know but names you don't. He's best known for his role in My Best Friend's Wedding. However, he also played a coworker-turned-crush for a few episodes in season 9 of Friends. He says he still gets complimented for his role as Gavin!
Christina Applegate
Christina Applegate was a fan favorite appearance, showing up in the series from seasons 9 to 10. She played Rachel's other sister, Amy Green. It was so beloved of a performance that she even earned an Emmy for Outstanding Guest Actress in a Comedy in 2003. You go, girl!