I view Jerome Kern as the greatest of all show tune commposers, he is poorly represented on Amazon, maybe better luck on ebay or iTunes.
The McGlinn EMI recording of *Showboat*, his masterpiece, is essential but not on Amazon.
It is worth getting but I have mixed feelings about it.
"Bill" is one of his best songs, the more stripped down the version the better, best is just piano and voice. "Can’t Help Lovin’ Dat Man" is another, worth downloading several versions of it and listening to it endlessly. "All the Things You Are" is another, "The Song is You," totally essential listening. "Whipporwill."
Getting excellent Kern requires some work, it is not well anthologized, sadly.
For Rodgers and Hammerstein, this is a very good Oklahoma:
This is the best Carousel, their most subtle show:
I find *South Pacific* pretty execrable.
Rodgers and Hart are excellent, but no single CD is a good anthology, try downloading "Have You Met Miss Jones?" but get the song, not a jazz treatment of it.
In general I don’t like Ella Fitzgerald versions of this stuff, though they are all over iTunes.
Gershwin is by far the best served on disc of these composers. I prefer the two-disc Sony set but there are many many good Gershwin recordings, here is the Sony, truly wonderful and fairly comprehensive:
His best show as a whole is Oh, Kay
Oddly this is still not so well known, I don’t know why not, download "Do, do do" from this show even if you don’t buy the whole thing.
I don’t consider *Porgy and Bess* "show tunes" but it is still excellent, even try the Miles Davis recording of it or many other jazz renditions. Simon Rattle does the best version of the opera.
Sondheim is a genius, here is the best CD of his, Side by Side, stripped down to piano and voice, I have listened to this so many times:
Most recordings of his shows are muddy and murky, disappointing. *Company* might be the best show as a whole but I keep coming back to that two-disc set.
Lloyd Webber has taken many whackings, but JCS is still wonderful, there is however only one worthwhile version, the original theater company, now only on expensive import but worth it, no more than 2x the price of a normal CD:
After that he is good only in bits and pieces, the shows get worse and worse.
That’s what comes to mind offhand.
Addendum: Tyler the Blogger might add songs like "How High the Moon," and "Cherokee," plus some Harold Arlen. Art Tatum interprets show tunes better than just about anybody. Cole Porter I do not love but he should not be neglected. Adam Guettel intrigues me, but he cannot light a candle to Magnetic Fields (Stephen Merritt), 69 Love Songs, volume one, essential listening for all.