A couple of my favourite jigs - Mac's Fancy / The Mist on the Mountain.
I learned these from a spectacular De Dannan record which is definitely worth purchasing legally over the internet if you are any sort of fan of traditional music that shatters your bones.
These are a couple of the several tunes that I learned by ear, a mean feat for someone as attached to sheet music (strangely known as 'dots' in the trad world) as me.
I try to learn all the tunes I can by ear, it takes longer than just quickly sight reading music (at which I am a master) but the end result is far better. The tunes trip from your fingers far more naturally and in an ideal world I wouldn't use sheet music at all.
Next weekend we're playing at a street party in Crickhowel for the Jubilee.