yourDictionary: Links to sites about the languages of the world and their dictionaries.
Omniglot: Languages of the world and their writing systems.
Ethnologue: Languages, language families, tells what languages are spoken in what countries.
Linguist List: Links about languages.
Latin
Latin–English dictionary, English–Latin word search and analyzer of declined word form.
Latin–English dictionary: Recognizes also word endings.
Dictionary of medieval Latin
Latin–English word list arranged by subject
Orbis Latinus: Latin and Romance languages.
The Latin Library: Latin texts, no translations.
Latin literature: Texts and translations (mostly English, French and Italian).
Lacus Curtius: Site about Rome and Latin literature. Contains e.g. Regio lists.
Philosophia Botanica: Linné's book about botany in Latin.
Neo-Latin texts
Abbreviations
Abbreviations
Romance languages
Orbis Latinus: Latin and Romance languages.
Romanian
Classic Greek
Greek–English dictionary, English–Greek word search and analyzer of declined word form.
English
yourDictionary: English Dictionary, tells also the etymology of words.
English etymological dictionary: You can also search by the etymological root of words.
Webster's Dictionary: Tells pretty much everything about a word.
Merriam-Webster: Dictionary and thesaurus.
Dictionary and thesaurus
Acronym Finder: Acronyms.
Anagrams
Sanskrit
Apte Sanskrit Dictionary: Sanskrit–English dictionary.
Capeller's Sanskrit-English Dictionary: Sanskrit–English and English–Sanskrit dictionary.
Celtic languages
A course of Welsh and Welsh–English dictionary.
Irish: Pronunciation, links to courses and dictionaries.
Gaelic
Dictionary of Gaul
The possible spellings and pronunciations of the word euro in Irish
Other Indo-European languages
Thracian
Etymological dictionary of Indo-European languages
The root words of Proto-Indo-European
Chronology of Indo-European people
Egyptian
Ancient Egypt and its language
Chinese
Zhongwen: The Chinese characters, word lists and some texts.
Japanese
WWWJDIC dictionary
Japanesepod101: A great site with Japanese lessons. A lot of its functions are free.
Other languages
Nostratic languages
Maori
Constructed languages
Richard Kennaway's list of constructed languages
List of constructed languages
Ardalambion: Languages of J.R.R. Tolkien.
Filology, etymologies
Etymological databases
The hypothetical proto-language of all the languages of the world: I won't decide whether one should believe it or not.
Numbers 1 to 10 in 5,020 languages
Common expressions in many languages
More common expressions in many languages
English words and suffixes derived from Latin and Greek
Behind the Name: Quite a good site, many languages, some categories, names of famous people, etc.
Birthcare: You can also search by the meaning of a name.
20000 Names: Names are organized according to language (51 of them), and the site also has many lists arranged by meaning.
The Baby Names Searcher: Says to have over 50,000 names. Free service allows only 2 searches at a time.
What's in a Name?: Origin of names, words and spells of Harry Potter books.
Omniglot: Languages and writing systems of the world.
Everson typography: Alphabets of European languages.
Ancient Scripts: Obsolete and still used scripts.
Runes
Runes
Ogham: An old Celtic alphabet.
Zhongwen: The Chinese characters, word lists and some texts.
Numbers of Greek
Numbers of Greek
Fonts
Unicode fonts for IPA symbols
Paleography
Abbreviations used by scribes
Punctuation
Errors made by scribes
Abbreviations used by Irish scribes
The Free Library: World literature in English. Double clicking of any word opens a new window with the meaning of the word.
Bibliotheca Augustana: Latin, Greek, German, English, French, Italian, Spanish, Polish and Russian literature.
All works of Augustine
Pages of medieval books
Oxford Text Archive
On-line Catalogues of Western Manuscripts
Bibliotheca Latina
Wikiquote: Quotes.
English
Philip Pullman
Bridge to the Stars: Philip Pullman fan site.
Beowulf: An English epic. Text is both in Old and Modern English.