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

• Ancestry Ireland (The Ulster Historical Foundation) 
• Emerald Ancestors (BMD Data)
• Roots Ireland (BMD Data from IFHF)
• General Register Office NI (GRONI)
• LDS Pilot Project - Irish Civil Registration Indices 1845-1958
• General Register Office Ireland
• Ros Davies' Co. Down, Ireland Genealogy Records
• Irish Genealogy (Free church records provided by Irish Government project)

Historical Societies

• North of Ireland Family History Society (Lisburn Branch)
• Ulster Architectural Heritage Society

Census, Wills, Military and other Records

• Public Record Office NI (PRONI)
• The National Archives of Ireland (1901 & 1911 Census)
• Belfast Family & Community History (1901 & 1911 partial census)
• National Archives (Kew)
• Griffith's Valuation

Street Directories

• Lennon Wylie Site
• Guide to Belfast & Ulster Street Directories (PDF)

Books, Reference texts

• My Roots, Tracing your Belfast Ancestors (Free PDF booklet)
• A History of Ulster, Johnathon Bardon, Blackstaff Press; 2nd Ed. (2005)
• The Irish in Britain, 1750-1922 (University of Bradford, Irish Diaspora Studies)

Generic Ancestry

• Ancestry.co.uk
• FindMyPast
• Family Search (from the LDS)

Guides to History

• The Plantation of Ulster (BBC)

Huguenots

• The Huguenot Society of Great Britain and Ireland