Useful Links:

Vikings
http://www.vikingsonline.org.uk/      http://www.cne-siar.gov.uk/museum/viking.htm
http://www.thorshof.org/edda.htm

For photographs of the 2006 large re-enactment of the battle of Hastings.
http://hastings.vikingsonline.org.uk/gallery.htm

Normans in Ireland
http://www.parle.co.uk/genealogy/early_ireland.htm
http://www.pdevlinz.btinternet.co.uk/JohndeCourcy.htm       http://tasi.org.uk/

This is a good one on castles and their development
http://www.users.globalnet.co.uk/~ctaylor/castles.htm

17th Century
http://www.devereuxs.org.uk/      http://www.fairfax.org.uk/

World War One
http://beck.library.emory.edu/greatwar/index.html      http://digital.lib.umn.edu/warposters/
http://www.ww1battlefields.co.uk/index.html

British
http://www.rirfus-museum.freeserve.co.uk/      http://www.1914-1918.net/index.htm

Irish
http://www.1914-1918.net/16div.htm      http://www.1914-1918.net/36div.htm
http://www.irishsoldier.org/ulster_division.html

Germans
http://www.users.hunterlink.net.au/~maampo/militaer/milindex.html

Ulster-American Folk Park
http://www.folkpark.com/links/

American Civil War
http://www.minstrelboys.org.uk/       http://www.civil-war.net/

Longbow Archery in Ireland
http://tasi.org.uk/