Best Album Purchase, or Best Evaluating Record


I would just like to know what you consider your best album purchase ever, or your choice of album used to evaluate a stereo system.

My best purchase has to be about 300 - 400 classical records, for $300, that contained many mint shaded dogs, Living Presence, and blue Backs (among others).
licoricepizza
bought an original Casino Royale in nm shape for $5 at a record show. Also bought a nm Die Beatles HorZu from the same guy for $5. He was going to knock a buck off the pair as well.
Whenever I do a tweak or an upgrade, I reach for the Diana Krall Christmas Songs LP, and not the 200g black version, but the 150g transparent red version. It sounds wonderful. It has everything--SOTA analog source recording, great mastering, female vocals, lush orchestrations, sleigh bells and assorted percussion.

I also have to give mention to "Class of '78," a direct-to-disc of the Buddy Rich Big Band. That's the record that launched my latter day vinyl craze. I took that LP and its companion SACD to my local high end store and had the sales guy spin them both through a pretty expensive all-Linn system. That was that and I haven't bought any digital music since, and I didn't even listen to any for over a year.
I really like the M&K Lp 'For Duke' as a reference recording..This LP really has some of the best sounds
recorded IMHO and shines on my system