The Oliver Cromwell Society has a website with basic information on the English Civil War. In light of the growing popularity of Warhammer Historicals' English Civil War miniature wargaming rules set, this could be useful in filling in some gaps players' knowledge.
This episode of Battlefield Britain focus on The Battle of the Boyne, fought in 1690 between the forces of the deposed King James II, and those of William III of England (Prince of Orange), who, with his wife Mary II (his cousin and James's daughter), had acceded to the Crowns of England and Scotland in 1688. The battle took place across the River Boyne near the town of Drogheda on the east coast of Ireland, and resulted in a victory for William. This turned the tide in James's failed attempt to regain the British crown and ultimately aided in ensuring the continued Protestant ascendancy in Ireland.