The Federal Election Commission keeps records of campaign contributions. It's not simple to track down who is contributing to political campaigns, but this website about Campaign Finance and Data is a good place to start.
The United States federal government is the largest research organization in the world. Much of their research is available online for free. Find background and updates on federal legislation through THOMAS. Find what the median income or educational attainment level is for your zip code is through Census.gov.
See what these free federal databases have to offer.