It all comes down to turnout, imho. This assumes a Romney win of about 52%-48% nationally, which is within the realm of possibility given the slight Romney edge among likely voters in some polls (particularly Gallup.)
I genuinely feel that Florida and Virginia will go to Romney, given their tendency to vote Republican except in years when the Democrats have won decidedly. Ohio, much less certain about, but hope that turnout will carry the state to Romney, albeit very narrowly. Wisconsin and Iowa are tricky to call also, but given that unemployment is very high in Wisconsin in particular, I tend to give Romney an edge here also, but again narrowly.
New Hampshire will stay with Obama, maintaining true to New England in general.
Early voter returns in Colorado give the edge to Romney there, while early voting in Nevada give the edge to Obama.