The Guild of Gentry and Allied Skills - UK-based group specializing in civilian life in 17th Century England, including but not limited to the English Civil War.
Jeff & Caroline's pages of 17th Century Stuff - Information for 17th century reenactors. Includes advice on being an artilleryman and musketeer, sewing and costumemaking tips.
The Siege Group - Englishmen reenacting the English Civil War (with occasional forays to later periods) with reference to the specific history of their venues. Schedule of events and contact information.
Tattershall Trayned Band - Elizabethan and English Civil War re-enactors based in the southwest USA. Includes details of how to make a matchlock musket.
17th Century Life And Times - A small society of two regiments concentrating on living history and small battle reenactment displays. Site has brief history and civil war timeline.