Mitch’s Wargaming and Model Making Blog has a short illustrated article on making an English Civil War style house. I’ve used similar techniques to build a town of houses for my Gothic Horror games.
Baccus 6mm has a good painting guide for the English Civil War. There’s also information on flags.
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.
Victory Without Quarter is a set of free wargames rules for quick play English Civil War battles.
This episode of Battlefield Britain covers the Battle of Naseby, fought on June 14, 1645. Engaged in the battle were the the main Royalist army of King Charles I and the Parliamentarian New Model Army, commanded by Sir Thomas Fairfax and Oliver Cromwell.