My first link was from the NY Times, but it was the A.P. press release. Here's the Times' obituary:

Mercedes Sosa, Who Sang of Argentina's Turmoil, Dies at 74

By LARRY ROHTER
Published: October 5, 2009

Mercedes Sosa, the Argentine folk singer whose politically charged repertory, sung in a powerful, earthy and impassioned alto voice, led her to be known throughout Latin America as "the voice of the voiceless," died early Sunday in Buenos Aires. She was 74.

Ms. Sosa had been admitted to a hospital in the Argentine capital two weeks ago, suffering from kidney disease and with liver and lung problems. Her death was announced on her Web site and by her son, Fabián Matus, who said: "Mercedes Sosa has lived her 74 years to the fullest. She did practically everything that she wanted to do."

In a career that spanned 60 years, Ms. Sosa became revered as both a victim of and a commentator on the political and social turmoil that afflicted her country and the rest of the continent. She was one of the pioneers of the "Nueva Canción" or "New Song" movement, a style of socially conscious music drawing on folk elements that first flowered in the 1960s, and enjoyed her biggest commercial success and political influence interpreting songs from that genre, like Violeta Parra's "Gracias a La Vida" and Horacio Guarany's "If the Singer Is Silenced."

"Mercedes Sosa is synonymous with struggle, resistance and freedom," the newspaper Clarín, Argentina's leading daily, stated in an online tribute to the singer that will also be part of a special section to be published on Monday. "Traditional and modern, rural and worldly, rough and sophisticated, she was nothing more and nothing less than the most important Argentine singer in history."

Haydée Mercedes Sosa was born in Tucumán, in northwestern Argentina, on July 9, 1935, the daughter of a day laborer and a washerwoman, and grew up in poverty. One of her grandfathers was a French immigrant, while the other was a Quechua-speaking Indian, and that mestizo background extended to her music, which drew upon and mixed both the Andean and the European song traditions.

Ms. Sosa's career began at the age of 15 when, singing a song called "I'm Sad" under a pseudonym, she won an amateur hour competition on a local radio station. It was not until 1962, however that she recorded her first full-length album. Over the next decade, Ms. Sosa, also known as La Negra because of her dark hair and Indian features, became more and more popular throughout South America, thanks both to her resonant, expressive voice and to her reliance on songs that commented on the problems and issues of the day.

But after the military seized power in Argentina in 1976 and installed a murderous dictatorship, Ms. Sosa, who was publicly identified with parties of the left, began having political problems and found many of her songs banned from the radio. She complained of being harassed, followed and threatened by police, military and paramilitary forces, and after she was arrested in 1979 and released following international protests, she went into exile, first in Spain and then in France.

She was able to go back to Argentina in 1982, as the hold of the Armed Forces was weakening. But Ms. Sosa's musical tastes had broadened during her years in exile, and after her return she became an early advocate of and mother figure for a new generation of singer-songwriters whose roots were more in rock 'n' roll and international pop than traditional or folk music. She quickly added songs by future stars like Charly García and Fito Páez to her repertory, giving their careers and music both credibility and an important commercial boost. She continued to champion emerging young talent until her death.

Ms. Sosa was married to a musician, Manuel Óscar Matus, for eight years, and later lived with Pocho Mazzitelli, who was also her manager, until his death in 1978. Fabián Matus is her only child.

As her international renown expanded, Ms. Sosa seized on opportunities to collaborate with performers outside of Latin America, like Luciano Pavarotti, Sting, Andrea Bocelli, Nana Mouskouri and Joan Baez. After touring with Ms. Sosa in Europe in the late 1980s, Ms Baez described her as "monumental in stature, a brilliant singer with tremendous charisma who is both a voice and a persona."

"I have never seen anything like her," Ms. Baez added. "As far as performers go, she is simply the best."

This year, Ms. Sosa released a two-CD set called "Cantora," or "Singer," that featured her in duets with more than a dozen Latin American and Spanish singer-songwriters, some of them young enough to be her grandchildren. The roster of participants is a who's who of contemporary Latin American pop, including Shakira, Julieta Venegas, Caetano Veloso, Joan Manuel Serrat, Joaquín Sabina, Gustavo Cerati, Jorge Drexler and Calle 13. An accompanying DVD has also been released, but hopes for a tour had to be abandoned because of Ms. Sosa's declining health.

"Cantora" has been nominated for three 2009 Latin Grammy Awards, including best album and best folk recording. Ms. Sosa, who recorded more than 70 albums and CDs, won the Latin Grammy for best folk recording three times, in 2000, 2003 and 2006, and has from the start been considered a favorite to win again at this year's ceremony, which is to be held in Las Vegas in November.

In recognition of her status as "the nation's most beloved voice," as Clarín put it, on Sunday afternoon Ms. Sosa's body was lying in state at the Argentine Congress building in Buenos Aires. According to Argentine press reports, her body is to be cremated on Monday in a private ceremony.

Outside the Congress building on Sunday, long lines of fans, ranging from artists who admired and copied her to the ordinary people who flocked to her concerts, waited to pay their last respects. "Thank you Negra, for your singing and your struggle," read the placard one man held aloft.