The first stop major reference work for Western classical music. Go here to get background information and context. Often a great please to start for traditional Music History papers.
Oxford Bibliographies Online give an overview of a topic, then an annotated bibliography of works on that topic. A great guide to use when starting your research or doing topic exploration. The music collection includes entries on composers, genres, and forms.
The librarian's biggest database for finding articles in music journals. Search here once you have narrowed your topic and want in depth, specific articles on music pieces, composers, concepts and periods.