http://registers.nli.ie/ Catholic Parish Register at the NLI.

Handwritten, can be hard to read, time consuming but so worth it. Because the records were kept by many, names can be spelled in various ways. For example, my Hassetts are spelled Hassan, Hassen Hafsen, Hassad, and Hassett. This is because of Anglicized spellings of Gaelic names as well as illiteracy.