My Congressional District gives you quick and easy access to selected statistics collected by the U.S. Census Bureau through the American Community Survey. The American Community Survey provides updated detailed demographic, social and economic statistics every year for the nation’s communities. With My Congressional District, you can view statistics covering age, employment, education, and much more. My Congressional District is powered by the American Community Survey and Census Application Programming Interface (API). They have a short video called DATA GEMS: How to Access Data for My Congressional District
GovTrack.us district maps leads to a Google map of a district
100 Years of US Elections in the database Social Explorer The presidential, senatorial, congressional and gubernatorial election data maps show "Election Competitiveness: Vote % Difference Between Democratic and Republican Candidates"
Ballotpedia has district and re-districting maps. The site is "a nonprofit and nonpartisan collaborative encyclopedia designed to connect people to politics. Featured information includes elections, politicians and candidates at all levels of government: elections, congress, state executive officials, state legislatures, recall elections, ballot measures and school boards. Ballotpedia is a wiki, which means anyone can improve it."
nationalatlas.gov has printable maps and raw data for congressional districts
Redistricting FairVote.org explanations and guide to resources "By gerrymandering the districts, legislators and their political cronies have used redistricting to choose their voters, before voters have had the opportunity to choose them."
Philadelphia Congressional District Maps Committee of Seventy