From George Clooney to Julia Roberts: The Best Guest Stars on Friends

It may be all about the core six, but the gang had many famous faces join them along the way

GEORGE CLOONEY & NOAH WYLE

The ER stars made an appearance on their fellow NBC show as a pair of doctors (of course) who try to date Rachel and Monica – after they've committed insurance fraud in the season 1 episode, "The One with Two Parts."