Brennan Center Report (6/06, 147 pgs, 612 KB) : www.BrennanCenter.org/programs/dem_vr_hava_votingsystems.html
Executive Summary (6/06, PDF, 21 pgs, 611 KB) : www.brennancenter.org/programs/downloads/SecurityExecSum7-3.pdf
GAO Report (9/05, PDF, 101 pgs, 1.3 MB) : www.gao.gov/new.items/d05956.pdf
Mythbreakers 2 (06, PDF, 62 pgs, 850 KB) : www.VotersUnite.org/MB2.pdf
Flyers & informational handouts : www.VotersUnite.org/info/flyers.asp
Wikipedia : Electronic voting,
Voting machine,
Voting system
Black Box Voting : Ballot-Tampering in the 21st Century (2004) : www.BlackBoxVoting.org/book.html
Electronic Voting and Democracy : www.Electronic-Vote.org (Italy)
Electronic Voting: Critical Issues, Critical Risks (download)
www.BallotIntegrity.org/Electronic%20Voting%20Critical%20Issues.doc
(This is a bit dated, but still provides good background.)