I. GENERAL RESOURCES
For the whole of Ancient Greek language, literature, history, geography, art and archaeology, the well-supported (NEH, Annanberg/CPB) Perseus, based at Tufts University, headed by Greg Crane: http://www.perseus.tufts.edu
Bibliography on the venerable Année Philologique, online for us through http://www2.coloradocollege.edu/Library/Reference/Classics.html
And, for language and literature up to the present time, the M(odern) L(anguage) A(ssociation) bibliography, online for us at http://www2.coloradocollege.edu/Library/Reference/CompLit.html
For gender and women's studies, the Diotima site pioneered by Suzanne Bonefas and Ross Scaife: http://www.stoa.org/diotima/ (Actually that whole Stoa site is worth exploring.)
Maria Pantelia of the T(hesaurus) L(inguae) G(raecae), based at UCal/Irvine, has a list of Electronic Resources for Classicists: http://www.tlg.uci.edu/index/resources.html
II. HISTORICAL MATERIAL
For ancient history (translated ancient sources), Paul Halsall's Ancient History Sourcebook at Fordham University: http://www.fordham.edu/halsall/ancient/asbook.html
For Byzantine history, including some images, Halsall's Byzantium site at http://www.fordham.edu/halsall/byzantium/.
For Athenian democracy in particular, Ross Scaife announces a new improved Demos site at the Stoa: http://www.stoa.org/projects/demos/home.
III. ARTS
Stefan Hagel at the Austrian Academy of Sciences has some fun and informative things about ancient Greek sounds: musical fragments in thin synthesized versions at http://www.oeaw.ac.at/kal/agm/, pronunciation including some Homer at http://www.oeaw.ac.at/kal/agp/, also some more Homer, sung with a harp at: http://www.oeaw.ac.at/kal/sh/.
The Greek Orthodox Archdiocese has a full site of Byzantine music, including some English instructional material at http://www.goarch.org/en/multimedia/audio/
An enthusiastic big site dealing with Rebetika (the Greek equivalent of Blues), is at http://www.rebetiko.gr/indexdb.asp
A computing guy called Alexandros has a lot of his favorite pop music available (for listening only, after you sign in and get a password) at http://alexandros.com/audio/realaudio.shtml.
IV. LANGUAGE
Donald Mastronarde has a page of alphabetic sounds for ancient Greek, keyed to his textbook, at http://socrates.berkeley.edu/~ancgreek/pronunchtml/pronunciation_guide.html
Philoglossia is a nice beginning Modern Greek course, with a page on the alphabet showing you how to write as well as pronounce the letters alone and in words: http://www.xanthi.ilsp.gr/filog/default.htm
Some film clips with vocabulary, helpful in learning Modern Greek, experimentally online at Yale (they'd like feedback).
To get your wordprocessor to write Greek, follow the advice of Amherst's IT dept or of Patrick Rourke (who explains more fully). You can also choose current, monotonic Greek wordprocessing (no diacriticals except the acute accent) from the Hellenic Resources Network. If you're using Perseus, there are special instructions for configuring your browser.
V. MODERN GREECE
The Ministry of Culture has a comprehensive site at http://www.culture.gr/welcome.html
More resources on modern Greece collected at the Cavafy Chair, University of Michigan: http://www.lsa.umich.edu/modgreek/links/
And at the Modern Greek Studies Association: http://www.hnet.uci.edu/classics/MGSA/links.html
The Greek Diaspora is interestingly represented by the Foundation for Hellenic Culture, http://www.foundationhellenicculture.com/index.html.
The Tsakopoulos Collection at Cal State/Sacramento has a links page, helpful for Greek American studies.
VI. NEWS LINKS
Greek and world news from a major Athens daily--the Daily=Kathimerini, English and Greek: http://www.ekathimerini.com/
Another major daily, To Vima (in Greek) http://tovima.dolnet.gr/
Various news and information from the Hellenic Resources Network, including a link to the Athens News Agency: http://www.hri.org/
The Athens News, an English language paper: http://www.athensnews.gr/
And, for novelty, the Akropolis News in Ancient Greek, conducted by the Catalan enthusiast Joan Coderch-i-Sancho from Barcelona: http://www.akwn.net/