Nigerians headed to the polls Saturday to vote for president, a week after parliamentary elections were marred by violence and accusations of fraud in Africa\'s most populous nation. Incumbent Goodluck Jonathan is the presidential front-runner despite a poor performance in the parliamentary and senate elections by his People\'s Democratic Party, CNN reported. His main challenger - former military ruler Muhammadu Buhari - was a contestant in the past elections in 2003 and 2007. Buhari is the candidate for the Congress for Progressive Change. Other candidates include Nuhu Ribadu and current Kano state governor, Ibrahim Shekarau.