The Oxford Handbook of the American Congress. It is an invaluable 2011 update on research in specific areas concerning the US Congress. Each of the essays reviews recent developments and points out areas where research is needed.
That book now sits (though is pulled off the shelf frequently), next to my copy of The American Congress Reader, published by the Cambridge University Press. The editors are Steven S Smith, Jason M Roberts and Ryan J Vander Wielen. It brings together some of the most important texts on the US Congress by academics. Some are full articles which have been published in scholarly journals, whilst others are extracts from books. There are 42 separate contributions.
The structure of this book of readings is
I The American Congress: Modern Trends
II Representation and Lawmaking in Congress: The Constitutional and Historical Context
III Congressional Elections and Policy Alignments
IV Members, Goals, Resources & Strategies
V Parties and Leaders
VI The Standing Committees
VII The Rules of the Legislative Game
VIII The Floor and Voting
IX Congress and the President
X Congress and the Courts
XI Congress, Lobbyists, and Interest groups
XII Congress and Budget Politics
XI Further Readings on Congressional Politics
I used this book a lot in directing my thinking and reading - and still do. Obviously some areas are more relevant to my own particular research interests - but this is a book to keep picking up, and extending one's knowledge.