The Roper Center for Public Opinion Research at University of Connecticut maintains access to a large inventory of exit data polls (1978-2000). You review some data online, but to do further analysis and access the raw data, you will need to contact our Electronic Data Center coordinator, Dr. Rob O'Reilly (firstname.lastname@example.org).
The American National Election Study is a great source for analyzing trends in electoral opinion, please see: http://sda.berkely.edu/archive.htm.
An African-American National Election Study was also conducted in from 1984-1996. Check these out at the ICPSR under the following study numbers: 1125, 2029, 9954, and 8938.