PhilPapers is a comprehensive index and bibliography of philosophy maintained by the community of philosophers. It monitors all sources of research content in philosophy, including journals, books, open access archives, and personal pages maintained by academics. It also hosts the largest open access archive in philosophy.
Covers all areas of philosophy (Western and non-Western) and provides brief definitions for philosophical terms and concepts, including terms from the related fields of religion, science, and logic. Also includes biographical information about major and influential philosophers.
The language is aimed at non-specialists to help explain the history, meaning, and importance of a concept or person. Excellent starting place for understanding new terms and concepts related to philosophy and logic.
IEP was founded in 1995 for the purpose of providing detailed, scholarly information on key topics and philosophers in all areas of philosophy. Authors of the articles are professors at colleges and universities around the world.
Over 2,700 articles, on everything from Medieval philosophy to Postmodernism, and from Aesthetics to Philosophy of biology. Provides in-depth essays about topics and people. Most essays conclude with bibliographic citations.
SEP is an open access encyclopedia, "designed so that each entry is maintained and kept up to date by an expert or group of experts in the field. All entries and substantive updates are refereed by the members of a distinguished Editorial Board before they are made public."