The Oxford Handbook of the American Congress (Oxford Handbooks) Lots of interesting articles about current research into Congress
Institutions Of American Democracy: The Legislative Branch (Institutions of American Democracy Series) Articles by some of the leading scholars on aspects of Congress
Parliament and Congress: Representation and Scrutiny in the Twenty-first Century Title says it all - and written by former Parliament of the House of Representatives and a former Clerk of the House of Commons
The European Parliament Deservedly, THE classic text on the workings of the EP, updated for 2011