The original Rhapsody in Blue
So, we talked about Gershwin's work in inspiring the Rhythm Changes, but his signature work is, of course, Rhapsody in Blue. One of my favorite recent finds is the original recording of Rhapsody in Blue, as preserved by the Internet Archive.
From the IA description:
This is the original recording of Gershwin's masterpiece, what may surprise many people is that it is an acoustic recording not electric one. This record was released soon after the piece was first performed and was soon replaced by a much more common electrically recorded record.