Ancient Greek
Liddell-Scott Greek-English Lexicon - perseus.tufts.edu
Liddell-Scott-Jones Ancient Greek Lexicon - wiki
Basic Lexicon of Ancient Greek - greek-language.gr
Etymologicon Magnum (1549 & 1816, Greek)
Etymological Dictionary of Ancient Greek - J.B. Hofmann (Greek)

Medieval Greek
Suda On Line: Byzantine Lexicography
Concise Dictionary by Emmanuel Kriaras - greek-language.gr

Modern Greek
Dictionary of Standard Modern Greek - greek-language.gr
Slang - slang.gr (Greek)
Greek slang - Vocabulary (Greek)
Dizionario grammatiche - B. Pianzola (1781, Greek -> Italian)
Little glossary about 1821 (Greek)
Lexicon of the current Greek language - S. Vyzantios (1835, Greek)
Vocabulary of Greek words derived from Turkish - K. Koukkidis (Greek)

Dialects
The Chian Vocabulary (Greek)
Lexique Khiote-Grec-Français (Chian -> Greek & French)
Etymological dictionary of the Aromanian language - K. Nikolaïdis (Greek)
Dictionaries and glossaries - lithoksou.net (Greek)

Greek pronunciation

Turkish
tureng - the multilingual dictionary (Turkish <-> English)
İngilizce-Türkçe Sözlük - dict.cc (Turkish <-> English)
Türkçe - Yunanca Online Sözlük (Turkish -> Greek)
Greek - Turkish Online Lexicon (Greek -> Turkish)
Sözlüksü (Ottoman -> English)
Turkish-Greek Lexicon vol. I - I. Chloros (Ottoman -> Greek)
Turkish-Greek Lexicon vol. II - I. Chloros (Ottoman -> Greek)
ekşi sözlük
Nişanyan - Türkçe Etimolojik Sözlük (Turkish etymological dictionary)

Miscellaneous
Venetian lexicon - El Galepin
Influenza della lingua Italiana sulla lingua Turca e viceversa - E. Aliotti
Etymological dictionaries of various languages - lexilogos.com