Open Secrets: Comprehensive Campaign Finance data source.
Follow the Money: Includes Gubernatorial, US Senate, US House, state-level offices, and Ballot Initiatives. Most comprehensive source for State Campaign spending.
Campaign Money: look up individual contributions, and look up contributions by zip code.
PACroyms: Acronyms of PACs registered with the Federal Election Commission. Helps users determine where money donated to campaigns from outside organizations originates.
Center for Responsive Politics: lists sources for state level campaign finance records
Follow the Money: National Institute on Money in State Politics: lists state level campaign finance contributions
iPoll: U.S. opinion polls on major issues, politics, and society (1930s to present).
Polling the Nations: International opinions polls.
Polling data can often be skewed and misleading. WNYC has a good tutorial about how to read polls for bias and poor design. Breaking News Consumer Handbook: Election Polls Edition.
Election Exit Polls: The Roper Center has downloadable exit polls.
Five Thirty Eight: Political analysis driven by data.
Google Trends: look at what people are searching in Google.
*read this before using Google Trends! It gives context behind the raw numbers (which can sometimes be misleading)*
PolicyMap: Data and mapping application that provides access to continuously updated data related to demographics, socio-economics, mortgages and home sales, health statistics, jobs and employment, education and more.
ProQuest Statistical Insight: Statistics published by the U.S. government and other agencies.
Social Explorer: provides easy access to demographic information about the United States, from 1790 to present.
For data from original research projects, look at the Research Tab.