Because we are all dorks, we do, in fact, have references! This is only partially complete; I will be adding more as I pull the information from all our collected books. (Did I mention we're all dorks over here?)
Cunliffe, Barry. The Ancient Celts. Oxford: Oxford University Press, 1997
Kenyon, Sherrilyn. Everyday Life in the Middle Ages: The British Isles, 500 to 1500. Cincinnati: Writer's Digest Books, 2000
Nagy, J. F. The Wisdom of the Outlaw. Berkeley: University of California Press, 1985.
Newman, Paul B. Daily Life in the Middle Ages. Jefferson: McFarland & Company, Inc., Publishers, 2001
Ross, Ann. Pagan Celtic Britain. Chicago: Academy Chicago Publishers, 1967
Webpages that I have not yet compiled into proper reference format, but good for perusing:
Celtic Studies Resources
Cyfraith Hywel - Mediaeval Welsh Law