Update Mar 2017: A better, more up-to-date repository of shapefiles is here
This project aims to catalog as many shapefiles of precincts (in some states "voting tabulation districts", or "election districts") across the United States. The priority is to obtain current shapefiles, namely more recent than 2010.
Please use the data to help with your projects, and if you find another state's shapefiles, please add it to the repository. If you have questions, email me at aaronbstrauss [at] gmail [dot] com.
Other resources. The Census reports provides 2010 and 2000 precincts lines for the country (by county). Professors Anasolabehere and Rodden matched 2010 shapefiles with 2008 data by state. These older shapefiles may be useful in areas of the country where precincts do not change often.