Excellent datasets at these sites:
http://www.umich.edu/~cses/ (comparative polling data; allows comparison of left-right support by demographic group across national lines; that makes it possible to operationalize how close a given country's party system is to producing 50-50 splits in major groups)
http://www.icpsr.umich.edu/cocoon/ICPSR/SERIES/00003.xml (American National Election Study site--also archived with useful material at http://www.electionstudies.org/)
http://www.icpsr.umich.edu/ (the parent data site, with historical election data on governors' races)
