I've had success here: http://www.rootsireland.ie/ They've made the records at the various county heritage centres searchable online. It includes baptism & marriage records from many parishes, Catholic & CoI. The site isn't free* but alot cheaper that a trip to Ireland.

* You buy "credits" in Euros with your credit card. To look at a page of search results costs 1 credit, to look at the details of one record costs 5 credits, if I'm remembering correctly. The whole credit concept is new so I'm not sure how it all works. It used to be free to look at search results page and 5 Euros to see the details.