Easy: any of Stereophile test CDs to check that your Left channel is Left...
Then the last chapter of "Get Better Sound" and CD "The Chieftains. tears of stone". If you do not want the torture of listening to Diana Krall and Joni Mitchell while tuning up your rig, then use Symphony No.3 by Gorecki (Electra Nonesuch 979282-2) while looking at Stereophile Buyer's Guide 2008, page 221). PM me if you need a copy of that article