what are the "must have" CD's


For years, I've invested in quality sound equipment and have a small collection of CD's of different types.....but I realize that there are problaby some "must have" CD's that really show just how good (or bad) a system really is. This isn't a quest for who your favorite female singer is...or what orchestra you like the best....I'm really after sonic quality and sonic range (gotta show off the sub and boomy rock probably isn't the best way to do it).

I'm open to suggestions in most any musical category...the only qualification is that the CD has to be readily available and not some collector's item.

If there is already a list somewhere..please point me to it....or post your suggestions.
ghstudio
Since there's some interest in "Americana" here, let me recommend "Heartworn Highways," a collection of informal recordings of some of the great Texas bards (Clarke, Earle, van Zandt), back in the day (mid 70s).

Great songs, and though the recordings seem to vary a bit across tracks, the sound is wonderfully natural. According to Stereophile, who named it a "recording to die for" the recordings are somewhat low tech; anyway, it really works. Highly recommended, if you like male singer songwriters.

John
Willie Nelson's "Moonlight Becomes You". Excellent great sounding renditions of several very classic standards. Simple, basic, accoustic, and very live sounding. A first rare recording.
Someone did mention ZZ Top's greatest hits,which is a very interesting recording. It does contain some very deep LF that most systems will %100 miss. I think it is more a test of room response than system quality. I could reproduce the LFs in a small apartment on an el cheapo system, but could not hear or feel them at my home with a "much better" system - what is up with that ? There is some very interesting stuff on this recording - see if you can find it.