Franz Liszt wrote a nice piece for bass trombone and organ, which can work well with either euphonium or tuba. It is the "Hosanna" and is based on a hymn tune with simple variations. It is a rather powerful work, but is not technically challenging. I have used it in church and it worked well. The sheet music is available here: Liszt Hosanna You can buy a recording of Christian Lindberg playing this and several other pieces that offer good ...