There's even some art music that tries to co-exist with the two traditions of western classical music, and popular music.

One example that leaps to mind immediately is the group "Rachel's", which blends, quite nicely, elements of 'rock' with 'classical' chamber music.

Handwriting is their first album, and a nice one, though perhaps more appealing to fans of rock music (not that it 'rocks', really). The band includes piano, strings, a drumkit, and (variously) electric and acoustic basses.

Music for Egon Schiele is program music for a stage production about the life of the late 19th century (IIRC) expressionist painter by the same name. It veers toward the classical side of things, and recalls the period represented by the storyline, without seeming derivative. Here Rachel's is represented only by piano, viola, and cello. As befits program music for a production about Schiele's life, the music reflects important moments in Schiele's life, such as the development of his relationship with one of his models.

The Sea and the Bells is an album with, at base, a nautical theme, somewhat coincident with the long poem (evocative of Pablo Neruda, who the group apparently have some affection for - his poetry is quoted on the Handwriting disc) contained in the liner notes. Here the music is more modern, more obviously a product of the 20th century classical tradition than the other albums. The ensemble is also larger than on other albums, including a larger palette of sounds. Also, the theme and the structure of the album as a whole are more strongly related.

Selenography, like Handwriting, is unthemed, consisting instead of a dozen or so separate pieces. Period-wise, the influences from classical music seem broader, and the rock elements are more prevalent. This is their most varied album: it contains a lovely harpsichord suite, songs using electronics, and even a spoken word performance.

I believe all of these are available on Quarterstick records, probably in the popular music section at an upscale music or book store, or who knows where at a good store which stocks 'indie' music.

This is only one tip of an enormous iceberg; art music is hiding all over the place, but all you have to do is look around a bit.