I'm not Irish, but my husband is, and my Ancestry.com newsletter had an article (by Juliana Smith) which said the following: "Ancestry.com has posted indexes to Irish Civil Registrations which began in 1864 for births, marriages, and deaths (1845 for non-Catholic marriages). In addition there is an index to births and baptisms that dates back to 1620, extracted from a variety of records.
Three other collections that were also posted caught my eye—Catholic baptisms, marriages, and deaths (the latter being the smallest). Although these collections are works-in-progress that are smaller in size and not all-inclusive, they are significant because some of the records pre-date civil registration. Since Irish emigration peaked during the famine and post-famine years prior to when most civil registration began, these records an important resource for many Irish-Catholic ancestors who left during that period."
Be sure to check it out if you have Irish roots!