California Classical Association (North)
The American Philological Association
BREPOLiS (databases available from Brepols) [subscription required]
The Greek Transcoder (for converting old Greek fonts such as SGreek to Unicode)
The Alpheios Project (integrated tools for Firefox that enable Latin and Greek dictionary-lookup on almost any site)
Diogenes (an open source program for searching the TLG and PHI databases)
Linux Libertine (an open source, high quality font with very extensive Unicode coverage including an almost complete polytonic Greek set)
Cardo (another free and attractive Unicode font, designed specifically for Classicists, so the Greek and even the metrical coverage is almost complete, but other areas of the font table can be a bit sparse)
Junicode (one more free and stylish Unicode font, primarily for Mediaevalists, but with a beautiful old-fashioned Greek character set; currently it has some spacing issues, and the extended Greek set is patchy)
SC Unipad (a great and customizable Unicode text editor for PCs; feel free to download my preferred Greek keyboard layout for SC Unipad [right-click, save-as])
The Silver Muse (hypertext system of bibliographies, commentaries, etc. for Imperial Roman poetry)
Pinax Online (a bibliography of online [ancient world] bibliographies...)
The Database of Greek Animal Sacrifice