In the context of this discussion, you might find this paper interesting:
Secret-Ballot Receipts: True Voter-Verifiable Elections
It's written by David Chaum, the cryptographer responsible for DigiCash, among other things. From his bio page on Wikipedia, I also found End-to-end auditable voting systems.
Update! Now it seems we can see if this really works: First Test for Election Cryptography.
Looking back in time now, I've read a couple of articles on the experiment in Takoma Park, and this system actually seems different from the one described in the original paper. However, it is still by David Chaum, and still supports the end-to-end audit properties. The system is called Scantegrity II.
