I'm not always in agreement with Andrew Sullivan, but he's nothing if not thoughtful, and a wonderfully expressive writer to boot. That's why I suggest that you read his piece on Obama in full.
But in case you don't, here's the gist of it:
But this much we can already say: Obama brings something no one else does to this moment. By replacing one of the most globally despised and domestically divisive presidents in American history with a young leader half-Kansan and half-Kenyan, America would be saying something to the world: Bush-Cheney is not who we are. America is not what it has come to appear to be. This country is among the most culturally and racially and religiously diverse on the planet. America has long been a powerful and vital beacon for human rights - not, as recently, the avatar of torture, rendition and executive tyranny. The simple existence of Obama as a new president in a new century would in itself enhance America's soft power immeasurably, just as a clear decision to leave Iraq would provide much greater leverage for diplomacy and military force in a whole variety of new ways. Obama would mean the rebranding of America, after a disastrous eight years. His international heritage, his racial journey, his middle name: these are assets for this country, not liabilities.
I couldn't agree more.