I guess I am playing nothing but fiddle tunes as I play mostly Celtic music, but heres a list of some of the things I am playing on my OM:
The Cameronian
Hardiman the Fiddler/Blackhaired Lass/An Phis Fluich
The Cliffs of Moher
Táimse im Chodladh
Carraroe Jig / Out in the Ocean / Garret Barry's Jig

What I find difficult is doing the rolls and cuts and some of the ornamentation, but its fun nonetheless.

Regards

Marc