Update (6:35 p.m. EDT): Via CNN, President Barack Obama's comments on Ride's death:

"As the first American woman to travel into space, Sally was a national hero and a powerful role model," President Barack Obama said soon after news of her death broke. "She inspired generations of young girls to reach for the stars and later fought tirelessly to help them get there by advocating for a greater focus on science and math in our schools. Sally's life showed us that there are no limits to what we can achieve and I have no doubt that her legacy will endure for years to come."

Update (6:25 p.m. EDT): The New York Times' obituary is online, and worth a look to help understand the significance of Ride's space travel as well as her contributions to the space program. For example, Ride was the only person to sit on the investigative boards for both the Challenger explosion in 1986 and the Columbia disaster in 2003.

Original: The first American woman to travel to space, physicist Sally Ride, died on Monday at the age of 61. The website for her company, Sally Ride Science, broke the news of her death, saying she died peacefully. She'd been battling pancreatic cancer for 17 months, her biography page at Sally Ride Science notes. Ride rode the Space Shuttle Challenger in 1983, at the age of 32, and again in 1984.  NASA also has a good remembrance and biography of her, with this nice passage: 

"Sally Ride broke barriers with grace and professionalism – and literally changed the face of America’s space program," said NASA Administrator Charles Bolden. "The nation has lost one of its finest leaders, teachers and explorers. Our thoughts and prayers are with Sally's family and the many she inspired. She will be missed, but her star will always shine brightly."

The Chicago Sun-Times notes that "she is survived by Tam O’Shaughnessy, her partner of 27 years; her mother, Joyce; and a sister, Bear." This appears to be the first time Ride and O'Shaughnessy were described as partners. A 2009 interview with them at the American Library Association refered to them as "good friends."