Redish, J. C., Chisnell, D., Newby, E., Laskowski, S., and Lowry, S., 2009, Report of Findings: Use of Language in Ballot Instructions, NISTIR 7556. (pdf)

Redish, J. C. and Laskowski, S., 2009 (originally prepared 2006), Guidelines for Writing Clear Instructions and Messages for Voters and Poll Workers, NISTIR 7596. (pdf)

Redish, J. C., 2005, Review of the gap between instructions for voting and best practice in providing instructions, Task 1 report to NIST. (pdf)

Voting and Usability, a project of the Usability Professionals' Association Includes links to many other excellent and important resources

Norden, L., Kimball, D., Quesenbery, W., and Chen, M., 2008, Better Ballots, New York University Brennan Center for Law and Justice.

A very important report. The page that leads you to the report also has links to more recent blog articles and other resources.

Ballot Usability & Accessibility. Dana Chisnell's blog. Great articles and also links to relevant slide sets from talks.