Liddell-Scott Greek-English Lexicon
Free online dictionary for Ancient Greek; outdated, but until recently the academic standard
The Cambridge Greek Lexicon - $
A much-needed updated edition of the dictionary above, currently only available by purchase
Discovering Ancient Greek and Latin
The Open University
"For those who have encountered the classical world through translations of Greek and Latin texts and wish to know more about the languages in which these works were composed."
Getting Started on Ancient Greek
The Open University
"Offers a taster of the ancient Greek world through the study of one of its most distinctive and enduring features: its language. The course approaches the language methodically, starting with the alphabet and effective ways to memorise it, before building up to complete Greek words and sentences. Along the way, you will see numerous real examples of Greek as written on objects from the ancient world."
University of Texas at Austin: Classical Greek Online
Brief lessons on the main grammar concepts and translating key primary sources (Homer, Herodotus, Plato, etc)
The Center for Hellenic Studies, Harvard: A Brief Introduction to Ancient Greek
Introduces basic concepts and key resources for the study of the language
JACT: Greek Summer School
Free open-access materials from the instructors of the Reading Greek textbook series
r/IntroAncientGreek
Mini/review lessons on key grammar concepts
Ancient Greek for Everyone
Free online course book
The Reading Greek Series
Reading Greek: Grammar and Exercises
The base textbook
Reading Greek: Text and Vocabulary
Practice translating passages
Reading Greek: An Independent Study Guide
The answers for the previous two books in the series
Speaking Greek
Audio CDs of the Text and Vocabulary sections