Georges-Denis Zimmermann: Songs of Irish Rebellion (Dublin, 1967) & (Philadelphia, 1967) (excellent)Colm O'Lochlainn: Irish Street Ballads (Dublin, 1939 and other editions) (excellent but historical prespective not always sound)
Michael Mulcahy and Marie Fitzgibbon: The Voice of the People (Songs and History of Ireland) (Dublin, 1982) (useful introduction but highly unreliable as to history and song texts)
John Moulden: Thousands are Sailing - a brief song history of Irish emigration (Portrush, 1994) - for opinion ask Liam's Brother or Martin Ryan or Antaine
There are other possibilities but they'll do for a start.