The British Legion
http://www.britishlegion.org.uk/

In Flanders Fields
http://www.inflandersfields.be

The Oxford University War Poets site
http://www.oucs.ox.ac.uk/ltg/projects/jtap/

Wilfred Owen
http:// www.hcu.ox.ac.uk/jtap/

Siegfried Sassoon
http://www.sassoonery.demon.co.uk

The BBC World War One site
http://www.bbc.co.uk/history/wwone

First World War.Com (contains many recordings of popular songs from WWI)
http://www.firstworldwar.com