Like everyone else says, Highlander Radio is the way to go. If you want a few legally downloadable tunes from a great new Celtic group, check out this website:
http://mp3.washingtonpost.com/bands/trasna.shtml

Trasna is a local Virginia group from Virginia's Shenandoah valley. The tunes are from their first CD and are samples (full songs, not just portions). They are a really high energy group, and the young lady who plays the fiddle is not only great looking, but very talented as well..