The Ultimate Demonstration Disc, Volume 2 (Chesky, of course) on SACD (also plays on a normal CD player). That's the "test" disc. Any new equipment, converters, power supplies, even cables (I know, but still). Every track is there for a specific reason, no two sound similar (if they do, you need better speakers). No overdubs, no compression in the signal path, no multi-tracking, no large format consoles. Total minimalism, freaky good gear in freaky good spaces. If there's a weakness in a system, this disc will find it. But you need to know what it sounds like on a system that's worthy of the recording. If that makes sense.
For something a little more "real world" (and one I keep with me to dial in rooms and unfamiliar PA systems) Britney Spears "Toxic" ("In the Zone" - Jive #53748 - If I recall, mastered by Tom Coyne). I don't care much for the tune (although I suppose I started to find it somewhat catchy over time), but the recording has most elements you'd want all in one package. Sparkly clean, down & dirty, a really excellent overall soundstage with a super-clear side component, uber-tight, dead-center bottom, in-your-face mono compatibility with super-dry, up-front vocals. When you really crank it up, I mean really crank it up, you'll notice your woofers orbiting in the weirdest way. And I mean smaller woofers too (this is the tune that I crank through my D4M's when people ask to hear them and almost without fail, they ask where I keep the subwoofer - which I don't have). There's clean, there's distortion (but "clean" distortion), there's low end, there's top end, there's an incredibly well-defined center, there's incredibly well-defined side information (and only a freakishly small amount of it, considering the apparent imaging), there's dynamic contrast, there's deep, if not overly-controlled low end. There's NOT a natural depth and holographic imaging like you'd find on UDD2 - but if you're looking for a tune that will quickly tell you if your system is up to the task (or a mix is up to the task on the same system), I don't know of too many other tunes that have the "Swiss Army" handiness of Toxic.
But no MP3's in either case. You need to hear the "whole" thing. 44.1kHz 16-bit is fine. But the top end (on both of these recordings) shouldn't be limited to 16kHz (as it would be with MP3). And don't even get me started on the space-monkeys.
And yeah, I guess if you don't have DSOTM and Aja, you shouldn't even consider yourself a human with ears.