1. William Grant Still
I discovered William Grant Still (1895-1978) when the orchestra I played in, the Fort Smith Symphony, recorded a CD of his works for Naxos. Called "the Dean" of African-American composers, Still wrote eight operas, a symphony, a tone-poem called "Africa," and many other works. He also arranged music for several movies. His music often uses blues progressions and rhythms. I found it beautiful, fun to play, and approachable.
While I was a graduate student at SMU in Dallas, my viola professor, Ellen Rose, commissioned a new viola concerto from Margaret Brouwer and premiered it with the Dallas Symphony. I had the chance to see how the relationship between a composer and performer can influence the development of an incredible piece of music. Brouwer's concerto was lyrical and full of gorgeous melodies, and she used a diverse array of tonal colors, especially from the percussion section. It's truly a beautiful addition to the viola repertoire.
3. Howard Hanson
Hanson directed the Eastman School of Music for forty years, and he received numerous awards for composition. I played his Symphony No. 2, "the Romantic." Its tonality is modern, but not strident, and it has many lush, expressive melodies. My husband commented that it reminded him of movie music, and I was pleased to discover it was actually used for the closing credits of the movie Alien, and John Williams used it as a model for the music in E.T.
4. Daniel Bernard Roumain
I performed Roumain's Darwin's Meditation for the People of Lincoln with the composer himself for a benefit concert for the victims of the Haitian earthquake. Roumain is a classically trained violinist and composer, but he's influenced by hip-hop, Haitian folk songs, and other contemporary music. A Haitian-American composer, Roumain brought boundless energy to the stage, yet his music was shadowed by tragedy, from Lincoln's battle against slavery to the present conditions in Haiti (Roumain is Haitian-American). Alternately haunting and vibrant, Roumain's music is well worth listening to.
5. Diane Thome
I discovered Diane Thome when I performed Like a Seated Swan, a piece for viola and computer-realized tape. She might be one of the most obscure and least approachable composers on this list, but her music is fascinating. Like a Seated Swan wove the warm richness of the viola into ethereal, other-worldly computer-generated sounds. The effect was compelling, if unusual.