Within your State your vote has a great deal of significance. Under the Electoral College system, we do not elect the President and Vice President through a direct nation-wide vote. The Presidential election is decided by the combined results of 51 State elections (in this context, the term "State" includes DC). Your vote helps decide which candidate receives your State's electoral votes.
The founders of the nation devised the Electoral College system as part of their plan to share power between the States and the national government, since the States report to the Nation, the States pick the nation leaders, but since the people report to the States they vote for their State. Under the Federal system adopted in the U.S. Constitution, the nation-wide popular vote has no legal significance. As a result, it is possible that the electoral votes awarded on the basis of State elections could produce a different result than the nation-wide popular vote. Nevertheless, the individual citizen's vote is important to the outcome of each State election. We are the United States of America, not the United Citizens of America, the states should be deciding.
Since the election of George Washington only once has a person won the Electorial vote and not the popular vote, and that was the election of 2000 between George Bush and Al Gore. Every other election in the history of the country (including the 2004 election) the winner of the popular vote did become president.