The best book is probably Sean Duffy, Brian Boru and the Battle of Clontarf (2013). There was an exhibition in Trinity College Dublin with a good site http://www.tcd.ie/Library/about/exhibitions/boru/index . pop

There is a short piece here http://www.historyireland.com/medieval-history-pre-1500/the-battle-of-clontarf-in-irish-history-and-legend/