The database, which is run by the Irish Family History Foundation, holds more than 20 million records including many church register transcriptions unavailable online anywhere else. Most of the counties of Ireland are included, but do be sure to check the list of records held by each of the county collections before you dive in!
The site operates on a credit system. The offer reduces the cost of viewing records from 25 to 15 credits, for which all researchers will give thanks.