The most acclaimed recording of Der Rosenkavalier is the one conducted by Herbert von Karajan for EMI with Elisabeth Schwarzkopf, Christa Ludwig, Theresa Stich-Randall, and Otto Edelmann. Nicolai Gedda sings the Italian tenor's aria. Available from amazon.com.
Maria Reining, Sena Jurinac,
Hilde Gueden, Walter Berry, Anton Dermota, Alfred Poell, Ludwig Weber,
Karl Böhm conducts a DG recording with a cast including Irmgard Seefried as Octavian, Marianne Schech as the Feldmarschallin, and Rita Streich as Sophie, that can be ordered from amazon.co.uk.
R.Strauss: Der Rosenkavalier
Christa Ludwig, Gwyneth Jones, Lucia Popp, Walter Berry, Placido Domingo, Wiener Philharmoniker conducted by Leonard Bernstein
My favorite visual version of the opera is available on DVD from amazon.com. It stars Felicity Lott, Anne Sofie von Otter, Barbara Bonney, and Kurt Moll. Anne Sofie von Otter is especially outstanding as Octavian.