The best synthetic work is Braddick's God's Fury, England's Fire. It has the benefit of being published by Penguin (therefore cheap), and being an excellently researched and well written book.

Other recommendations would be based on what you are interested about the war. Interested in the military history? Peter Gaunt, The English Civil War: A Military History. Want to know about people's experience of the violence of the war? Charles Carlton, Going to the Wars: The Experience of the English Civil Wars, 1638-1651. Want to know about the rise of radical religion? McGregor and Reay, eds. Radical Religion in the English Revolution. Want to know about the rise of political radicalism? Christopher Hill, The World Turned Upside Down.

There are certainly more books to recommend, but it depends on where your interests lay.