There are 11 counties in the US (plus 3 independent Virginia cities) that voted for Obama this year but haven't voted for a Democrat in a presidential election in over 50 years...if ever. A few of these counties, as you'll see below the fold, went solidly for Obama, by more than 10 points.
Here's a list of the counties, the percentage point margin of victory for Obama (in some cases, could still be provisional) and the last time they voted for a Democratic presidential candidate (if known--I only have data back to 1928).
Henrico County, Virginia (suburbs of Richmond): 12.3% (last Dem win: 1948)
Kane County, Illinois (outer suburbs of Chicago--includes Aurora): 11.1% (last Dem win: before 1928!)
DuPage County, Illinois (suburbs of Chicago--very populous and generally high-income): 10.7% (last Dem win: before 1928!)
Carroll County, New Hampshire (rural east): 6.4% (last Dem win: before 1928--and given NH's Republican history before '28, could be never)
Kendall County, Illinois (SW edge of the Chicago metro area): 6.3% (last Dem win: before 1928!)
McHenry County, Illinois (NW edge of the Chicago metro area): 5.3% (last Dem win: before 1928!)
Jefferson County, Alabama (Birmingham!): 5.1% (last Dem win: 1952)
Carroll County, Illinois (rural NW): 4.8% (last Dem win: before 1928!)
Gallatin County, Montana (near Yellowstone): 3.4% (last Dem win: 1944)
Waupaca County, Wisconsin (somewhat rural, central): 3.3% (last Dem win: 1936)
Teton County, Idaho (near Yellowstone): 0.8% (last Dem win: 1948)
And here are the Virginia cities in this category:
Harrisonburg (northwest): 16.3% WOW! (last Dem win: 1940)
Hopewell (near Richmond): 11.9% (last Dem win: 1952--odd that the last win was in a year when the Republican won)
Staunton (northwest): 2.2% (last Dem win: 1940)
Some Obama Counties That Haven't Voted Dem for President Since '64
Of course, there are a lot of counties that haven't voted Dem since the landslide victory in 1964. I won't list them all, but the ones that voted for Obama by more than a 10-point margin are worth mentioning...
Monroe County, Pennsylvania (northeast, lots of small towns that collectively have over 100,000 people): 17.0%
Prince William County, Virginia (outer suburbs south of DC): 15.9%
Dallas County, Texas (yep, Dallas): 15.6%
Washoe County, Nevada (Reno): 12.6%
Arapahoe County, Colorado (suburbs east of Denver): 12.1%
Tippecanoe County, Indiana (Lafeyette/Purdue): 11.6%
Also, the city of Manassas, Virginia can be included, with its 11.4% margin of victory for Obama. It separated from Prince William County (listed above) in 1975 and hasn't voted for a Democratic presidential candidate until now.
And an honorable mention should go to Harris County, Texas (Houston), the 3rd largest county in the US, which voted for Obama by a 1.6% margin (hasn't voted Dem for Pres since '64).
Note that a lot of these counties are quite populous (and, in many cases, growing)...and will be beneficial for the Democratic vote in the future!