Jed, Mudcat's own Philipa turned me on to a book titled "A Thousand Years of Irish Poetry". And in it I found any number of poems that I recognised as having later been set to music. In fact I am currently working my way through it looking for something that speaks loudly to me that I can set to music. Yeats is featured prominently, as you might suspect. But there is much to be gleaned from any number of ancient and modern poets. It is out of print, but a search will find copies easily.
All the best,