Five books should be in every Irish family historian's library; so says IrishCentral, and most researchers would agree:

Tracing Your Irish Ancestors 4th edition, by John Grenham

Surnames of Ireland, by Edward MacLysaght

Tracing your [County] Ancestors series, by various authors

A New Genealogical Atlas of Ireland, by Brian Mitchell

Tracing Your Irish Family History on the Internet, by Chris Paton

More details can be found here.