Ray Liotta - Charlie Metcalf, 'Time of Death', 2004

Liotta won an Emmy for his portrayal of a dying man in this episode, which was shot in real time, depicting not only the details of his treatment, but his memories of a wasted life.

Bradley Whitford - Sean O'Brien, 'Love's Labor Lost', 1995

Whitford would later become known as Josh Lyman in 'The West Wing', but here he played a young father whose wife died in childbirth after Dr Greene made a terrible mistake.

Forest Whitaker - Curtis Ames, six episodes, 2006-7

Ames blamed Dr Kovac for his debilitating stroke. First he tried to sue for malpractice, then resorted to intimidation and kidnap, finally killing himself in front of Dr Kovac.

Rosemary Clooney - Madame X, 'Going Home', 2004

George Clooney's aunt, a notable actress and singer during the 1950s, played an Alzheimer's patient who believed it was 1948, and tried to convince Dr Carter to appreciate the era's music.

James Woods - Dr Nate Lennox, 'Body and Soul', 2006

Nominated for an Emmy for his performance as a professor with Lou Gehrig's disease; his battle with the debilitating condition was shown through a series of flashbacks.

Alan Alda - Dr Gabriel Lawrence, five episodes, 1999

Lawrence arrived in the ER as a senior doctor, but after a series of mistakes it became clear that he was suffering from Alzheimer's. The performance earned him an Emmy nomination.

Ewan McGregor - Duncan Stewart, 'The Long Way Around', 1997

Quentin Tarantino directed this episode, in which McGregor and his partner rob a convenience store. Nurse Hathway was caught up in the shootout.

Kirsten Dunst - Charlie Chiemingo, six episodes, 1996-7

Dunst played a drug user and teen prostitute, whom Dr Ross tried to take under his wing after she arrived in the ER following a brutal assault.

James Cromwell - Bishop Stewart, four episodes, 2001

Cromwell played the churchman who, while being treated by Dr Kovac, helped the Croatian doctor come to terms with his faith after the death of his family in the Yugoslavian conflict.

Susan Sarandon - Nora, 'Old Times', 2009

While viewers phwoared at Clooney's return, Sarandon gave a moving performance as a grandmother who must decide whether to donate her dead grandson's kidney to Dr Carter.

Zac Efron - Bobby Neville, 'Dear Abby', 2003

Before 'High School Musical' made him a household name, Efron played a teen shooting victim who died after Nurse Lockhart's advice to the doctors about his treatment was ignored.

Rebecca De Mornay - Elaine Nichols, five episodes, 1999

De Mornay's character was a cancer survivor; she had a brief, melancholy affair with Dr Carter, who was her ex-husband's cousin.