Macmillan / Gale Virtual Reference Library.
Available online. (W&L subscription)
This second edition (2008), consisting of nine volumes, is the major revision of the first edition of this title and its predecessor. It specializes in coverage of "scholarship and fields that have emerged and matured since the publication of the original international edition," containing "nearly 3,000 entirely new articles... contributed by thousands of scholars (including several Nobel prize winners)." You may view the table of contents here.
Links will be maintained in several locations in the library Web site, including here.