Joe, Rita Streich was a 'light' opera singer, with a voice that was capable of popular and 'folk' song as well as the operatic 'tricks' (perhaps the best control of vibrato I have ever heard.

Try that recording sometime- Rita Streich- Volkslieder und Wiegenlieder.

Listen to her "Silent Night" on youtube. A clear voice with excellent diction.
http://www.youtube.com/watch?v=Mky2Adob8c0
Or the old Japanese favorite, "Sakura."
http://www.youtube.com/watch?c=MCWJqtz0LE&feature=related