The Stanford Encyclopedia of Philosophy--and especially the bibliographies provided for each entry--is an excellent place to begin researching philosophical topics. The Internet Encyclopedia of Philosophy and 1000-Word Philosophy are two other good, peer-reviewed resources.

The Baylor Libraries philosophy research guide contains BU-specific information about philosophy research, including contact information for the subject librarian for Philosophy. 

The websites for philosophical professional organizations, such as the American Philosophical Association, the American Catholic Philosophical Association, the Society of Christian Philosophers, and the Society for Phenomenological and Existential Philosophy also contain or link to philosophical resources.

Resources for specific groups (e.g. undergraduates, the Pre-Law Concentration, the Philosophy and Medicine Concentration, graduate students) can be found on the page for that group.