Oprah Winfrey, who is endorsing presidential candidate Sen. Barack Obama, the Democrat from Illinois. She hosted a fundraiser for him at her California estate that brought in an estimated $3 million. But that may be the least of what Winfrey offers. She has millions of TV viewers, a magazine, and other media holdings. Her book endorsements already have a huge effect on what Americans read, or at least what books they buy. And Winfrey says that no other candidates will be invited on her show.