Here's an argument from Daniel Koffler that he is:
Whereas Clinton has recently taken to pulling protectionist stunts and rethinking the fundamental theoretical soundness of free trade, and Edwards is behaving like the love child of Huey Long and Pat Buchanan, Obama instinctively supports free trade and grasps the universe of possibilities that globalisation opens up, and seamlessly integrates it into his "audacity of hope" theme. As he remarked in a recent debate: "Globalisation is here, and I don't think Americans are afraid to compete. And we have the goods and the services and the skills and the innovation to compete anywhere in the world."
More at the link. (HT to Jonathan Dingel) I've been reluctant to express an explicit view on any of the candidates, but speaking very generally, I think Obama has a better grasp of, and appreciation for, markets than the other Democrats and many of the Republicans. (When I say that, I have in mind a very specific point he made in one of the debates. I can try to dig it up if people want to know what it is.)
-- Ben Muse takes an empirical look at the issue of who is more pro-trade, here.
-- As for my point about Obama's understanding of markets, Greg Mankiw has a post that explains the issue and I agree with his take on it: http://gregmankiw.blogspot.com/2008/01/pigou-club-watches-debates.html