Free to all readers, the Stanford Encyclopedia of Philosophy "was 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." SEP is a dynamic resource, growing each year to incorporate new research.
Unlike the Stanford Encyclopedia of Philosophy, Gale is an e-book that mirrors its physical cousin. This means you can search its index to locate page-specific references. Its articles may contain different insights or sources than SEP, so it may be worth consulting both encyclopedias.