ATLA Religion Database Index compiled by the American Theological Library Association to books and periodicals covering all aspects of religion and related topics.
Arts and Humanities Citation Index (WOS) A major multidisciplinary index to research journals in the arts and humanities, including religion. Covers 1975 to the present.
Philosopher's Index The major index for philosophy. Many religious figures are often considered philosophers so this is also a good index to search for figures like Aquinas, Buber, etc.
JSTOR Full text of scholarly journals in arts and science, humanities, and social sciences. Current journals are not entered into the database for 2 to 5 years. Searchable by topic or by journal name. Can also browse by discipline -- Religion, Philosophy, Jewish Studies, Middle East Studies, etc.