According to Nate Silver (fivethirtyeight.com), Obama has a better than 90% chance of winning each of the following:
California
Connecticut
Delaware
District of Columbia
Hawaii
Illinois
Maine
Massachusetts
Michigan
Minnesota
New Jersey
New Mexico
New York
Oregon
Pennsylvania
Rhode Island
Vermont
Washington
He leads by double digits in most of them. In Connecticut, he leads by about 9, in Oregon and Pennsylvania by 7, and in Michigan by 3. Michigan looks pretty close but the Romney camp seems to have concluded they can't win it. Probably, "Let GM fail," dooms him there.
If Obama wins all those, that gives him 237 electoral votes. Ignoring the states that are leaning Romney's way, Obama needs 33 more electoral votes from:
Colorado -- 9
Florida -- 29
Iowa -- 6
Nevada -- 6
New Hampshire -- 4
Ohio -- 18
Virginia -- 13
Wisconsin -- 10
If Romney hits a grand slam between now and election day and wins all those states, he gets to 301. If he takes them all plus Michigan -- 317. That would be the absolute best case, dream scenario for him, and probably would require some catastrophic economic news, or a major Obama screwup.
Best case scenario for Obama: he sweeps the eight battleground states above, plus North Carolina (where Romney holds a narrow lead), and gets to 347. Or if Romney somehow finds a way to blow Missouri too -- 357.