I've probably given the most thought to the foreign-policy views of the two presumptive nominees, but the nature of our terrible economy seems to dictate that the economy will play just as big a role, which is good news for Obama and the Democrats (actually, at this point practically any issue is good news for Obama and the Democrats).
At any rate, McCain claims that he will offset tax-cuts with spending cuts, something that Republicans have claimed every election for a long time. He talks a good game about cutting earmarks from the budget, but the truth is they only amount to $20 billion (which will not be easy to get rid of), while his tax-cuts amount to $300 billion. One gets a better idea of his plan from the fact he hired Phil Gramm, who played a role in paving the way for the foreclosure crisis.
Obama's economics seem pretty much center left, even Clintonian. This is evidenced by his recent appointment of Jason Furman. This article in the New York Review of Books talks pretty extensively about Obamanomics.
As this post argues, I wouldn't worry to much about Obama's economic centrism.
One thing I wish Obama would talk more about is regulating financial markets. It's good politics (Obama can further tie McCain to failed Republican policies by pointing out Phil "Foreclosure" Gramm's role in the financial crisis) and good policy: it can be done without to much more spending, and could help head-off future financial crises.