Languages

Gaelic: Gaelic and Gaelic Culture. Info on Gaelic and Gaelic language resources.
Gaelic Dictionaries Online: Pointers to Irish, Scots and Manx dictionaries.

Scots Gaelic

Sabhal Mór Ostaig: Scotland's Gaelic-medium college on the island of Skye provides both online and local resources for Scots Gaelic learners.
Comann an Luchd-Ionnsachaidh: The Gaelic Learners' organisation. Information on joining CLI.
Scots Gaelic: Lessons and contacts for learning Scots Gaelic.
An Comunn Gaidhealach UK
Carmina Gadelica: Sections of the Carmina in Scots Gaelic and English.
Am Braighe: A newspaper (primarily in English) that intends to be a meeting place for Gaels and anyone interested in Scottish Gaelic language and culture. There is a Gaelic learners section and a bookstore with selection of Gaelic and English books.
Akerbeltz - A' Ghobhar Dhubh: Resources for learners including a dictionary of Gaelic idioms and expressions, MP3 files to hear the proper sounds and other resources.
TAIC: Gàidhlig lessons with audio files so you can hear pronunciations

Manx Gaelic: Manx Gaelic: Chengey-ny-Mayrey Vannin, resources for Manx Gaelic & Manx studies.
Recortyssyn Gaelgagh - Manx Archive: Manx Gaelic articles, lessons, texts and more.
Manx Language, Politics and Culture: Manx lessons, dictionary and more.

Welsh: A Welsh course by Mark Nodine.
Welsh-L Archive: Database of Welsh-L messages.
Cymdeithas Madog: the Welsh Studies Institute of North America, Inc., is dedicated to helping North Americans learn, use and enjoy the Welsh language.
Welsh Joint Education Committee Web Site: A consortium of the local education authorities (LEA's) in Wales offering a bookshop and other support for the Curriculum Cymreig.

Brezhoneg - Breton Language Page: Online lessons, summer course info and pointers to Breton resources.

Cornish Language Fellowship: An information source for people who do not speak the language to find out more, but to also provide Cornish speakers and students with online tools and a community centre.
Gernewek 101: An online phrase book for learning Cornish.
Gerlyver Kernewek-Sawsnek: A short lexicon of the Cornish language

Interactive Irish Lessons: Lessons from Learning Irish by Mícheál —ó Siadhail, along with audio clips.
Irish Language Reader: Nancy Stenson Workbook and Michael Rhodes' Irish Gaelic readings.
Focal an Lae: The Word of the Day in Irish by Dennis King. Provides back words from the Focal an Lae list and links to Gaelic resources.
An Doras: This journal of Gaelic culture offers articles in Gaelic and language instruction.
Conradh na Gaeilge Shasana Nua (The Gaelic League of New England): Information about Irish language classes throughout the six New England states of the northeast USA. Excellent links section.
: Texts and Audio in Gaelic
The Story of MacDatho's Pig: Side-by-side Irish and English from an Emory class in Irish.
Voyage of Bran: This medieval Irish saga was translated into English from the Old Irish by Kuno Meyer in 1890. Available in English or Irish Gaelic with criticism.
Literature and Verse: Pointers to ancient Irish tales and sayings, literature and more.
Irish Gaelic Song Archive: Gaelic songs and information on singing styles and singers.
CELT: Corpus of Electronic Texts: Contemporary and historical Irish documents in literature, history and politics. Texts in Irish Gaelic, English, Latin, etc.

Galician Language Institute: Galician is a Romance Language (not Celtic anymore), that belongs to the Iberianromance family of languages. It has common aspects with portuguese (morphology and some vocabulary). In Galicia, Galician and Castilian are both recognised as official languages.