To mark the 90th anniversary of the Passchendaele offensive New Zealand History online has launched a major new feature which explores the impact on New Zealanders of one of the First World War’s most tragic battles. The site includes film clips, oral histories with veterans who were there, interactive slide shows of contemporary images (many never before published) and graphs and maps.
You can find books about Passchendaele listed in this Voyager search. The Historical Abstracts database is a useful source for finding journal articles about the battle.