"I first met her on the set of Julia [in which she starred with Vanessa Redgrave]. She was a little girl but already beautiful and graceful. It didn't surprise me that she became such a talented actor," Fonda said.
Ralph Fiennes appeared with the actress in the 2005 period drama "The White Countess."
"For everyone who knew and loved her, Natasha's death is a terrible, devastating loss. She was a star. A great actress, a beautiful woman, a fiercely loyal friend, a brilliant and generous companion. She was an adoring and loving wife and mother. She was unique. My thoughts and prayers go out to Liam and her beautiful sons, Micheál and Danny and to all her family," Fiennes told ABC News in a statement.
"I cannot imagine a world without her wit, her love, her mischief, her great, great talent and her gift for living. I loved her very much. She was a supreme friend. I shall miss her deeply."
"Natasha is irreplaceable," actress Mia Farrow said in a statement to reporters. "I cannot think of anyone kinder, more generous, thoughtful, smarter or more fun. She is the godmother of two of my children. The Neesons and Vanessa [Redgrave] have always made me feel a part of their wonderful family. My thoughts and prayers are with them."
"Natasha was brilliant, beautiful, funny, talented beyond measure, as emotionally raw as she was razor sharp," said Jodie Foster, who co-starred in 1994's "Nell" along with Richardson and Neeson. "May Liam, her beautiful boys and her loving family hold her close as they move through this tragic moment."
"She had an incredibly luminous quality, that you seldom see, and a great sense of humor," Dame Judy Dench said in a statement to reporters. "I thought she was a really great actress."
"We spent one amazing day on a boat with my whole family and she and Liam and the boys," Joan Rivers said in a statement to reporters. "They were such a family. I mean just shouldn't have happened. And they made such a good-looking couple too. He doted on what she said, she doted on -- it was just perfect."
Sam Mendes, who cast Richardson as Sally Bowles in "Cabaret," remembered her mastery of her craft.
"Natasha combined the best of Redgrave and Richardson: the enormous depth and emotional force of a great actor on the one hand, and the intelligence and objectivity of a great director on the other," he said in a statement to reporters. "She was one of a kind, a magnificent actress. She was also an amazing mother, a loyal friend, and the greatest and most generous host you could ever hope to meet. It defies belief that this gifted, brave, tenacious, wonderful woman is gone."
Richardson was a member of one of Britain's most famous acting dynasties. She was the eldest daughter of Oscar-winning actress Vanessa Redgrave, 72, and director Tony Richardson.
Her father passed away in 1991 due to complications with AIDS. She had long been a supporter of AIDS-related charities, including amfAR, on whose board she had served since 2006.
Asked to comment on her skiing accident before Richardson's death was announced, a representative for amfAR told ABCNews.com, "Our thoughts and prayers are with Natasha and her family right now. Obviously, we're very saddened and disturbed by this news."