Back in October 2007, Clinton was beating Obama in Maine by a hilarious 47 to 10 margin, but it seems he's carried the state today, once again by a large margin. My understanding, though, is that this doesn't really count because it's a small state, much as Utah doesn't count because there aren't many Democrats there, DC doesn't count because there are too many black people, Washington doesn't count because it's a caucus, Illinois doesn't count because Obama represents it in the Senate even though Hillary was born there, Hawaii won't count because Obama was born there. I'm not sure why Delaware and Connecticut don't count, but they definitely don't.
Realistically, Clinton seems to have difficulty winning anywhere she can't mobilize racial polarization in her favor. Obama has, of course, deployed polarization to his benefit in a number of states (South Carolina, Georgia, Alabama, and Louisiana most notably) but he's also dominated the states with very few black voters.
...Obama's win in Missouri, of course, doesn't count because the state was called too late.