Perhaps moreso than any other 20th-century Spanish composer, Rodrigo seemed have an almost peculiar attraction (musically speaking, of course) to soprano voices. This is evidenced not only by his output for soprano voice, but also by his dedication of over 50% of his songs to these particular sopranos. I have compiled a list here of most of the singers of whom he spoke most fondly in my research. Victoria de los Angeles and Teresa Berganza are certainly of the more visible in the group, but others who enjoyed fame in the 50s and 60s may be available on vintage recordings. I personally recommend Victoria de los Angeles' 2-CD set of Spanish song from the Renaissance thru the 20th century. Enjoy!
Victoria de los Angeles