Here are some links we've found useful. Please update me if you find any which are broken, or want to add your site or another to the list. Please reciprocate by adding Baldock and Letchworth Blues, Folk and Roots Club to your links page.
Digital Tradition/Mudcat - database containing thousands of traditional songs. Includes an excellent forum for discussing traditional music
Yet Another Digital Tradition - DT mirror with GIF and ABC files
Jack Campin has a comprehensive selection of links; a useful site for 17th and 18th century music
John Chambers' ABC page - includes a web-wide ABC index and Tune Finder
Wild Dismay website - traditional tunes from the website of the band Wild Dismay - in GIF, MIDI, ABC format
Morris Tunes - another library of Morris Tunes in ABC
Nottingham Music Database - a resource for the NMD, in ABC and maintained by James Allwright
ABC Tunes from Cranford Publications - some collections of Cape Breton tunes, from the playing of such renowned fiddlers as Brenda Stubbert
Celtic Orbis- site for Irish and Scottish tunes
Dan Beimborn's collection of tunes in GIF and MIDI format
The Kitchen Musician website - with MIDIs and GIFs of tunes as well as links to instrument-related and other sites.
The Contemplator - lyrics and MIDIs for traditional tunes. Includes Barry Taylor's MIDI tunebook of Irish tunes
Traditional Music Library - A huge and very comprehensive list of traditional music resources.
My Song Book - tunes and lyrics on Henry Kochlin's site