soc.culture.scottish: Newsgroup FAQ
220+ pages, 485+K information. Updated daily. The most popular site on the internet for Scottish cultural information: history, arts, language, food, news, tartans, festivals, politics, education, sport; Links.
http://www.siliconglen.com/scotfaq/

CelticWonder
Glorifying Irish music in its entirety with RealAudio clips from Clannad, Anuna, Riverdance, Loreena McKennitt and others, as well as graphics, MIDI files, and a discussion board.
http://www.celticwonder.com/

Ceolas Celtic Music Archive
The home of Celtic music on the net, with reviews, biographies, guides, audio samples, hundreds of links to real-world and Internet resources, tunes, schedules, and instrument guides.
http://www.ceolas.org/ceolas.html

The Irish Music Forum
A bulletin board site dedicated to Irish Music.
http://cgi.tripod.com/music_irish/cgi-bin/YaBB.pl

Ancient Music of Ireland
This page discusses Ancient Irish music with an emphasis on the Bunting Collection of harp music (1792). There are several good MIDI files.
http://pybertra.club.fr/ceol/homepage.htm

Celtic Roots
BBC Scotland site covering Celtic, traditional and folk music from Scotland and beyond. Includes gig listings, reviews and programme information.
http://www.bbc.co.uk/scotland/musicscotland/celticroots/

Celtic Music - New Zealand
A resource for Celtic (Irish and Scots) musicians and performers. Information about events and sessions, teachers, and a tune collection.
http://www.celticmusic.co.nz/

Celtic Music
Wikipedia article explores the difficulty in defining a genre which includes the traditional musics of the Celtic peoples, and recorded popular music with only a superficial resemblance to folk styles.
http://en.wikipedia.org/wiki/Celtic_music