Barnes, James A., Michael Barone, Richard E. Cohen, and Charlie Cook.  The Almanac of American Politics 2016. Bethesda, Maryland: Columbia Books Inc., 2015.

The Almanac of American Politics is an exceptional resource that has been published every two years since 1972. It includes political background on each state and the voting records of every Congressperson and Senator on lots of important legislation. It also includes ratings of each member of Congress by various interest groups, from the most liberal to the most conservative, as well as on issues like environmental protection. It is a gem of a resource.