Some very useful resources :
Fiddle and Alternative Strings Forum – an excellent site for all string players.
Learn traditional fiddle tunes the FAST, EASY, and FUN way! – Another excellent resource for all fiddlers. Run by the mighty Michael Kelly!
Fiddlerman – another excellent resource. This site is run by a very good fiddle player!
Fiddle Hangout – another very good fiddle site.
Violinist – A good site for all things violinistic …but there are fiddle players there too 🙂
Fiddling Around the World – Excellent site by violinist / fiddler Chris Haigh.
Violin Master Class – The Sassmanhaus Tradition for Violin Playing.
The Session – A site devoted to Irish Traditional Music