A Latin Dictionary, by Lewis and Short, still the standard for Classical and post classical Latin, is online, and searchable in both English and Latin, thanks to the Perseus Project.
The IntraText Digital Library contains over 700 texts. Mostly medieval and renaissance.
The New Vulgate Bible (Nova Vulgata). The Vatican has made available to the public its revision of Jerome’s Latin bible. They have tried (with arguable success) to “fix” some problems in Jerome’s text, while staying close to the vocabulary and spirit of that important work. It is definitely more readable in places.
Thesaurus Musicarum Latinarum. An evolving database of the entire corpus of Latin music theory written during the Middle Ages and the Renaissance
An Analytic Bibliography Of On-line Neo-Latin Texts. Over 9000 listings for Latin texts written during the Renaissance or later.
Latin Place Names. This alphabetical site was established by the bibliographic Standards Committee as a resource for librarians—and you
The Ancient Library. A collection of scanned classics reference works from the 19th and 20th centuries, including Smith’s massive Dictionary of Greek and Roman Biography and Mythology, and Edwards’ English-Greek Lexicon.
Latin Lexicon compiled by David Morgan of Furman University. Extensive English-Latin list of modern terms, also organized by category, for ease of use.
Vocabula Computatralia. Ever wanted to know how to say “modem” in Latin?
Tolle, lege. Helpful reading and vocabulary for the beginning/intermediate Latinist. Helpful list of the 1400 most common Latin words.
De Imperatoribus Romanis. Read about the Roman Emperors (in English).
the 1911 Encyclopedia Britannica provides much useful information to the Latinist.
the Catholic Encyclopedia is also a great resource for the Latinist, especially this early 20th C. (i.e. pre-Vatican II) edition.