The Gershwin Etudes by Earl Wild — Earl Wild (who was a student at Carnegie Mellon many moons ago) wrote, I believe, 7 of these. All work listening to. All on wonderful Gershwin tunes. Search out the others.
I’ve Got Rhythm is probably one of the most important pieces in the history of jazz harmony, Open any book on Jazz Harmony, and there will be chapters on blues, chapters on modal harmony, and probably a whole chapter on “Rhythm Changes”, that is, the chord changes, and variations, to I’ve Got Rhythm. The only other piece that comes close to such importance in Jazz Harmony is “Giant Steps” by John Coltrane, which I’ll have to play some other morning.