Lovers of traditional Irish music will want O'Neill's in book form. A facsimile edition of "1850" is now published by Mel Bay. An edition of "1001" is published by Waltons. I don't know if "Waifs" is in print. Here are some places online to look:
Music of Ireland ("1850") Dance Music of Ireland ("1001") Waifs and Strays of Gaelic Melody
The Whistle Shop amazon.com Barnes & Noble Mel Bay
If you have additions to this list, or any comments or corrections for any of the tunes here, send me mail.