1. Oprah Winfrey

The most powerful woman in entertainment might just be the most influential woman in America. Consider this: University of Maryland economists estimate that Winfrey's endorsement of then-Sen. Barack Obama brought him 1,015,559 votes in the presidential election.

Winfrey says she isn't planning any political moves in her own future, but maybe that's because she -- and her expanding Harpo Inc. universe -- are just too busy. In 2007 the company pulled in $345 million in revenue thanks to a dizzying array of Oprah-branded media. While down a tiny fraction in the ratings, "The Oprah Winfrey Show," which launched in national syndication 22 years ago, has been the No. 1 syndie talk show for roughly 500 consecutive weeks, drawing 44 million viewers weekly in the U.S. alone.

"Oprah Winfrey Presents: Mitch Albom's For One More Day" landed in the Nielsen Top 5 last December, and "Oprah's Big Give" debuted there as well in March. Each issue of her O: The Oprah Magazine is read by 16.6 million people, making it the third-largest monthly magazine on U.S. newsstands. There's even an Oprah Store, which launched online in November, a satellite radio channel and a Broadway production success ("The Color Purple" closed in February after 910 performances).

Perhaps most significantly, Winfrey will soon have her own 24-hour namesake channel, OWN: The Oprah Winfrey Network, set to launch in 2009 or early 2010 in an estimated 70 million homes. But numbers insufficiently convey the full scope of Winfrey's cultural sway. She remains the single most listened-to woman in the country, singular in her ability to bring a product or a pet cause to the national stage. In short, what Winfrey thinks matters to a whole lot of people. Take all this, add in her noted philanthropy through the Oprah Winfrey Foundation, and you get perhaps the greatest individual success story in the history of the entertainment business.