Friends of the Mountain Dulcimer - A fantastic on-line community for mountain dulcimer players! Full of advice, tunes and videos, plus you get to meet really friendly and helpful contributors.
Everything Dulcimer - An excellent web site that contains a wealth of information, videos, dulcimer music TAB and an active dulcimer forum.
The Nonsuch Dulcimer Club - is a UK based organisation for anyone interested in hammered, or mountain dulcimers. The club was formed in 1993 by a small handful of hammered Dulcimer players, but soon extended its activities to also incorporate mountain dulcimer. It now has over 200 members who play one (or both) of these instruments.
Friends of American Old-Time Music and Dance - is a UK association for old time music playing and dancing. FOAOTMAD run a number of old time events each year and have a presence at a majority of bluegrass festivals around the UK. If you are interested in playing traditional fiddle tunes on your mountain dulcimer and want to play with fiddlers, banjo players etc or for Appalachian dancers then FOAOTMAD is an excellent starting point.