The fine Decca recording conducted by Maazel and his Cleveland Orchestra. Decca SET609-11. Also on London 13116. From 1975. Is a TAS Superdisc. Great Decca sonics. Somebody did a reissue (not sure who). The originals are pretty easy to find. Willard White is Porgy, Leona Mitchell is Bess.
I would add Simon Rattle's rendition with the LPO, on EMI. A very good reading recorded in the late 80s now available in the series great recordings of the century. As a fan of the opera, I gather you already have Miles Davis' album -- epic!