Here are some good places for information and statistics/data about elections:
- American National Election Studies
Survey of voting behavior in the United States, conducted biennially since 1956.
- Election Information
Contains official vote counts for federal elections from 1920 to present.
- Roper Center
The Roper Center for Public Opinion Research is one of the world's leading archives of social science data, specializing in data from surveys of public opinion.
FairVote is a nonpartisan, nonprofit organization that conducts research and advocacy for electoral reform in the US.