Best Classical to "broaden" listening arena?

I have come to "love" Yanni, Norah Jones, Sade, Sarah Brightman, etc.

Since I really appreciate individual instruments & have a fairly high end system with separation as a strong point--I am interested in which composer / group I should start my "classical" specific collection with?

On Audiogon, Classical seems to be the highest sold category thereby indicating high collectibility & listening by educated music lovers.

Thx in advance for your opinions,

Dr David Joned