Wildwood Flower/Reuben JamesWhistling Rufus
Great Speckled Bird/Wild Side of Life/It Wasn't God Who.../etc., etc.
Londonderry Air/Danny Boy
The Limerick Tune - I thing it's properly called Celita Lindo, but not sure...."Ay, Yi, Yi, Yi, your mother swims after troopships..."
The Ship That Never Returned/Wreck of Old 97/Super Skier/MTA
Ashokan Farewell (no, really, just having been overdone doesn't change the quality of the tune, just makes people sick of it)
That isn't 12, but it's what I can think of right now.
P.