Oprah's career as host of "The Oprah Winfrey Show" has spanned decades, making for many memorable moments. In conjunction with the announcement of ceasing production of her talk show in September 2011, the woman who has come to be known as Lady O selected her "Top 20 Moments."

Of all of the celebrity guests she has welcomed to her studio, one in particular stands out. Oprah nominated Mary Tyler Moore as her "Favorite Celebrity Woman" for her surprise appearance in 1997. A dedicated viewer of "The Mary Tyler Moore Show," Oprah was inspired by Mary and blown away when she unexpectedly read her name on the teleprompter to cue the star to walk on stage.

Oprah has launched several projects that she holds very close to her heart. In 1996, the famous "Oprah's Book Club" was established to promote literacy and inspire people to read. To this day, viewers continue to rely on Oprah's advice on what book to pick up next. With the evolution of technology, the book club has grown into an interactive forum for the host to connect with fans by means of Skype.

Founded in 1997, the Angel Network set out to raise money to afford 50 students the opportunity to attend college. By the conclusion of that television season, $3.5 million was raised.

Lady O not only makes dreams come true for others, but some of her own wildest dreams have come to fruition. In 1997, Oprah took the show on the road to join Tina Turner on her Wildest Dream Tour, giving her the opportunity to sing and dance on stage with the musical icon.

Doing what she does best, the always generous queen of daytime famously gifted her entire audience with cars in 2004. Her production team handpicked each member of the studio audience on the basis of them needing a car. Much to their surprise, they drove home from the show after being given the keys to a Pontiac G6.

To see the rest of Oprah's "Top 20 Moments," visit Oprah.com and keep checking back to ETonline for updates on Oprah's big announcement.

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