Loeb Classical Library - a virtual library of all that is important in Greek and Latin literature, with up-to-date texts and accurate English translations.
This resource provides free access to several Greek dictionaries, including The Online Liddell-Scott-Jones Greek-English Lexicon. It requires a login, but the account is free.
If you have a topic, this is an excellent place to start your research because it contains everything published in the field of classics, both articles and books. A detailed subject tree is also available to help you limit your search.
This website is describes itself as " ...a resource for information on women, gender, sex, sexualities, race, ethnicity, class, status, masculinity, enslavement, disability, and the intersections among them in the ancient Mediterranean world."
Print and ebook versions of the essential guide to all aspects of the ancient world - political, economic, philosophical, religious, artistic, and social.
From the Ancient World Online (AWOL): This includes links to materials for learning not only ancient Greek (Homeric, Classical, or Koine) and Latin, but also Sanskrit, Hebrew, Aramaic, Armenian, Egyptian hieroglyphics, Sumerian, Hittite ...
The home of the revised Ancient Greek Tutorials by Donald Mastronarde, adjusted to conform to the changes made in the second edition of Introduction to Attic Greek (University of California Press 2013) and to provide additional supplements to that book.