The Green Papers has details on elections as well as an archive on elections going back to the 2000 election.
CQ's Vital Statistics on American Politics has historical tables of primary and election results-- it's useful more as a guide to sources than actual numbers for this project.
100 Years of US Elections in the database Social Explorer The presidential, senatorial, congressional and gubernatorial election data come from Dave Leip's Atlas of U.S. Presidential Elections. Building on our recent release of 2004-12 election data, these maps now span over a century: presidential elections 1912 to the present, gubernatorial elections (including off-year elections) from 1990 to present, and congressional elections from 2000 to the present. The election data are displayed down to the district and county levels. Click here to get started with the maps. In addition to winners and voter turnouts, the maps also include voting age population, citizens of voting age population, and competitiveness.
Statistics for presidential elections by state can be found in the print reference book America Votes in both Paley Library and Ambler Library Reference Departments at call number JK1967.A8
America at the polls : a handbook of American presidential election statistics Paley Reference JK524.A73 and Congressional Quarterly's Guide to U.S. elections JK1967.C662 1994 go back to 1956.