Mary Travers of the popular folk trio Peter, Paul, and Mary died after a years-long battle with leukemia. She was 72. In the early '60s, Travers joined Peter Yarrow and Noel "Paul" Stookey to make music that mixed acoustic guitars with liberal politics. Their version of the Pete Seeger song "If I Had a Hammer" became a civil-rights anthem, and they performed the song at the 1963 March on Washington. The band recorded several Top 10 albums, and scored a No. 1 hit with "Leaving on a Jet Plane." The trio continued performing together until just a few years ago, when Travers was no longer able to perform because of her illness. Peter and Paul didn't sing her part, and were delighted when the audience would sing it for them.