What I use for reference music pretty much depends on what mood I'm in. My listening tastes run to 40% or 50% classical, with the rest fairly eclectic -- blues, folk, jazz, rock and so on, though my interest in classic rock seems microscopic when compared to others on forums like this.
My reference recordings tend toward straight acoustic material (voice & instrumental), or when instruments are amplified, a straightforward miking of the amp with minimal post-processing.
For example, The Great American Mainstreet Band has a brilliant recording of early 20th century jazz titled "Silks & Rags" - one of the best recordings I've ever heard. Also excellent are the Norbert Kraft classical guitar albums, the recordings by The Empire Brass, Tea Time Ensemble, the Thomas Tallis Scholars and dozens of others.
On the folk & Americana side, Jorma Kaukonen is well recorded, as are most albums by Janis Ian, Lydia Ruffin, Maura O'Connell, The Waifs and others.
For rock & blues, I often find the recordings by lower profile bands give a better sense of realism than the big names. The latter are often grossly overprocessed. I've got copies of some of the original unprocessed studio open reel tapes from the Ozark Mountain Daredevils and they are far better than the LPs. Going back, I've got a 1965 release by Lightning Hopkins that was nothing more than a couple of mikes set up in some no-name Texas studio that is absolutely intimate in its unprocessed rawness. If you want to hear musicians in your living room, start with a recording that hasn't had every gimmick thrown at it that is available in a fancy studio.
But, that's just me. I'm rather contrarian about such things.
