Of course, the standard repertoire isn't just about audition music. It's also what orchestras typically play for concerts, and it definitely determines what soloists they hire. Since many orchestras are highly risk averse, that means few of them are willing to take a chance on hiring a soloist to play, say, Ernest Bloch's lovely Suite for Viola and Orchestra. In fact, it's rare to see any soloists at all who aren't playing violin, piano, or cello. Where are the lovely concertos for flute, or oboe, or clarinet? I've heard Vivaldi trumpet concertos performed, but only rarely, and surely there are guitar concertos out there that aren't Rodrigo's Concierto de Aranjuez (though if there are, I've never heard them or seen them performed).
It's not that the standard repertoire isn't beautiful. I love a thrilling performance of the Beethoven "Emperor" Concerto or the Tchaikovsky Piano Concerto as much as anyone. But I wish that I could see more performances of rare, less well known works, including pieces by modern or obscure composers. While I've played in the orchestra for Beethoven's Violin Concerto many times now, I've never heard a live performance of the violin concertos by Janacek or even Bartok (not with an orchestra, anyway). I've seen a few pieces at their world premieres, including an exquisite new viola concerto by Margaret Brouwer and Tea: A Mirror of the Soul, an opera by Tan Dun. Yet, it bothers me to think that many amazing pieces like these have a grand premier, then end up forgotten and rarely performed again.
I'd like to see more musicians exploring and performing music outside the great standards. It's up to us to search out hidden gems and obscure treasures, and share them with the world. Even well loved composers often have pieces that for whatever reason, never make it into our recitals (when was the last time you heard a performance of J.S. Bach's Viola de Gamba Sonatas, instead of one of his Cello Suites?). There's a wealth of music out there, and we often only barely scratch the surface of this vast repository of history, culture, and art. It's time we looked farther and went deeper.
What are some neglected pieces of music you've discovered? What composers do you think deserve more attention than they're usually given?