If you need an overall guide to how to research vocal music, these tools are all great, depending on your specific need. They can lead you to other books about your song/topic. There are also many similar guides for individual composers. Ask the librarian if you need help getting started with research.
Reference sources help establish basic information, such as the definition of an unfamiliar music term or the dates of a composer's life. These are not generally considered scholarly sources (with the exception of the Grove Dictionary of Music and Musicians and the Garland Encyclopedia of World Music) and do not necessarily need to be cited or quoted from in research papers or projects.