Going back in time to find ancestors, the following is a list which might be of use to the genealogist.
The Irish 1911 Census: 1911 Census
The Irish 1901 Census: 1901 Census
Tithe Applotments (circa 1830)
Religious Census 1766 (not available for everywhere)
Books of Survey and Distribution (approx 1664)
Pendars Survey 1659
Street Directories: Street Directories for Cork
Registry of Deeds (from 1708): Registry of Deeds
For high profile names, Burke’s Landed Gentry (various publications) and Burke’s Peerage (various) might be useful.
O’Harte’s Pedigrees has many surname lists of genealogical usefulness.