Lyrics for THE COW THAT ATE THE PIPER can be found in Irish Come-all-ye's by Manus O'Conor (New York: The Popular Publishing Company, 1901) and Irish Song Book No. 2 (New York: Wehman Bros., 1909). The lyrics are pretty close to what has already been posted.

A storyteller's version, partly prose and partly verse, can be found in Irish Minstrels and Musicians by Francis O'Neill (Chicago: The Regan Printing House, 1913).

A much longer prose version of the story can be found in Legends and Stories of Ireland by Samuel Lover (Dublin: W.F. Wakeman, 1831)--The link takes you to a recent digitized copy.