The Latin Library
The Latin Library is a large collection of online Classical, Medieval, and Neo- Latin texts.
Perseus Digital Library
The Perseus Digital Library is a resource for both Greek and Latin texts and also contains dictionaries and images.
PHI Latin Texts
A searchable concordance of most Latin texts written before 200 AD as well as some Late Antique texts prepared by the Packard Humanities Institute.
Dizionario di Abbreviature Latine
Compiled by Cappelli and published in 1912, this book (available online for free) is by far the most comprehensive guide to Latin abbreviations.
Latdict is an online Latin dictionary that uses a wide variety of sources ranging from the OLD to books on specialized vocabulary. It features informative definitions and a vast vocabulary.
Whitaker's Words
A comprehensive and widely-used free online Latin dictionary.
Study Guide to Wheelock's Latin
A free, online text designed to accompany Wheelock’s Latin (4th ed.) written by Dale A. Grote (author of the Comprehensive Guide to Wheelock’s Latin).
LatinPraxis is a set of exercises and informative pages that correlate with Wheelock’s Latin. It also features useful vocabulary expansions for those who wish to enhance their Latin vocabularies.
Textkit is a compilation of free Latin and Greek texts, grammars, and textbooks.
An extensive, searchable database of over 450,000 Latin inscriptions.
Glossarium mediae et infimae latinitatis
Du Cange’s glossary of medieval and late Latin is a pioneering work in the study of languages and is still invaluable to many scholars today. Note: it is only available with a French interface.