http://lexicity.com/language/greek/ is an incredible compendium of dozens of online Ancient Greek resources, as well as other ancient languages!
http://www.perseus.tufts.edu/hopper/search is useful for both dictionary searches as well as the “Word Study Tool,” allowing you to look up words’ dictionary entries and oblique cases alike.
https://philolog.us is the dictionary extension of the Perseus website, allowing you to search the finest Ancient Greek dictionaries. Be sure to enter your word in the dictionary format, nominative singular.
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0007 Though not strictly an online resource, Herbert Weir Smyth’s Greek Grammar is a massive tome containing all of the nuts and bolts of the Greek language.
https://apps.apple.com/us/app/protagoras-classics-lexica/id1116707290 The Protagoras app is a compact dictionary app with an easy-to-use interface, allowing you to search in both directions (English to Greek and Greek to English) in a number of Ancient Greek dictionaries. It is, however, exclusive for Apple products.
http://www.perseus.tufts.edu/hopper/collection?collection=Perseus:collection:Greco-Roman is a little chaotic, but don’t let that intimidate you! This website is a collection of myriad texts, ancient and modern alike.
https://www-loebclassics-com.oxy.idm.oclc.org/ is an excellent digital library, containing works by hundreds of authors in the original with side-by-side translations. Use your Oxy credentials to log in and access the collection.
https://www.youtube.com/watch?v=qI0mkt6Z3I0, a lengthy and lovely recitation of a part of Book 6 of Homer’s Iliad.
https://www.youtube.com/watch?v=4hOK7bU0S1Y is a good segment on Ancient Greek music, and a very useful piece of the puzzle.
Also check out https://www.youtube.com/watch?v=6JFa8BZt2B0, https://www.youtube.com/watch?v=OcHWvl16mpg, https://www.youtube.com/watch?v=FsnjzDAuOAc and https://www.youtube.com/watch?v=kpmCE0XKNko
for more on the double-reed pipe, or aulos.
https://www.youtube.com/watch?v=4UWBo0rsuHU for info on the other side of Ancient Greek music, the kithara (origin of our very own guitar).
https://www.youtube.com/watch?v=mQKRAJTgEuo Whatever you might think of him, here is Boris Johnson reciting the beginning of the Iliad like a professional:
https://rhapsodoi.org/index-of-ancient-greek-recitations/ Last, but not least, here is the website of the Society for the Oral Reading of Greek and Latin Literature, or SORGLL, with a heaping helping of recitations in Ancient Greek.
Engage with the material culture of Ancient Greece by viewing Greek art, architecture and more at the following websites: https://www.metmuseum.org/toah/keywords/ancient-greek-art/
https://artsandculture.google.com/usergallery/greek-art/5QJygV8aLh0dLg
For an introduction to what some of the fieldwork in Classics might look like, check out the Centre for the Study of Ancient Documents. The link is to their own guide to epigraphic and papyrological resources: https://www.csad.ox.ac.uk/links
A directory of art and artefacts from ancient site, courtesy of Perseus: http://www.perseus.tufts.edu/hopper/artifactBrowser
http://www.typegreek.com is a fantastic and useful website allowing you to type in Ancient Greek with ease! Refer to the Alphabet Key to figure out how to include breathing signs, accents, iota subscripts and more.
A few quick reads on the alphabet: https://www.ancient.eu/Greek_Alphabet/, https://www.britannica.com/topic/Greek-alphabet
This one is just for fun: a side-by-side list comparing forms of Proto-Indo-European and its descendants, Sanskrit, Latin and Ancient Greek! https://allthingslinguistic.com/post/162178453172/latin-ancient-greek-and-sanskrit-triplets
Here is a collection of principle parts from Smyth’s Greek Grammar.
http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0007%3Apart%3D5&force=y