Here are some links to some significant research resources for Irish genealogy. Remember that only a small part of existing records have been digitised so to be thorough you should visit local archives, family history centres, graveyards, libraries etc. You cannot do comprehensive genealogical research purely over the Internet and certainly not without spending any money.

Irish Birth, Marriage & Death Records

Historical Societies

Census, Wills, Military and other Records

Street Directories

Books, Reference texts

Generic Ancestry

Guides to History