Congressional Quarterly has been producing this excellent guide to Members of Congress and their districts (States for Senators) since 1981. A biography is supplied of every member, with lots of statistics on the member and their district. Details of key votes and scores are given on 'party unity'; 'presidential support' plus the ratings by four advocacy groups
AFL-CIO - a federation of labour unions.
Americans for Democratic Action - liberal
Chamber of Commerce - founded in 1912 as "a voice for organized business"
American Conservative Union
There is a host of other information - including the order of seniority in each House; Youngest and Oldest Members; Women in Congress; Minorities in Congress - even "Members Who Have A Twin". Membership lists of groups within Congress (New Democrat Coalition; Blue Dog Coalition; Progressive Caucus; and the Republican Study Committee) are given - as well as details of committees.