The ballot used for the recently-held Southern Sudan referendum is the simplest ballot that has ever been used: see http://www.flickr.com/photos/usaidafrica/5386993117/
There were only two words that appeared on it: "unity" and "secession" (written in Arabic and English). There was also a symbol to assist the illiterate: two hands clasped together to symbolize "unity" and a single open hand to sybolize "secession".
Perhaps the most ingenious idea was that ballots are marked by a thumbprint. This makes fraudulent ballot-casting more difficult because each mark must be unique, but because there is no fingerprint registry in Sudan, the ballots are also anonymous.