This site has wonderful 95 page book (.pdf) of fiddle tunes collected by Bernie Waugh as well as abc files for the tunes. It is well worth a visit for anybody interested in fiddle tunes.
This website provides information about hammered dulcimer events in the Michigan area, where this is a very high concentration of interest for this particular instrument. There is also a repository of sheet music and midi files for traditional and original (tradtionally inspired) songs as well as links to various other resources within and outside of the hammered dulcimer community.
This is a search engine that is tuned to finding music on the web. Are you looking for sheet music, ABC format or a MIDI file for a particular tune? Give this a try.
This site contains a good collection of fiddle tunes, all available as PDF files with fairly clean notation. An added benefit are the associated MIDI files to play along with.