Another great resource added to the internet: The Jewish Encyclopedia.
This website contains the complete contents of the 12-volume Jewish Encyclopedia , which was originally published between 1901-1906. The Jewish Encyclopedia, which recently became part of the public domain, contains over 15,000 articles and illustrations.
This online version contains the unedited contents of the original encyclopedia. Since the original work was completed almost 100 years ago, it does not cover a significant portion of modern Jewish History (e.g., the creation of Israel, the Holocaust, etc.). However, it does contain an incredible amount of information that is remarkably relevant today.
Of linguistic interest is, for example, the immensely detailed article on the Hebrew alphabet. Obviously any remarks about the “earliest” this or that should be taken with a grain of salt in a century-old source, but it’s full of information, like the discussion of how the cursive script developed. (Via plep.)