Some of these that are being said are likely exaggerated, although I don't have numbers to back me up.
My guesses:
San Diego
Phoenix
Jacksonville
New Orleans
And that's about it. Cities like Pittsburgh, Las Vegas, San Antonio, Tampa, Indy, Pittsburgh...these would have been good guesses in the 80's, 90's, and early 2000's, but their trends would indicate that most whites in these cities are voting Democratic now.
Pittsburgh whites voted overwhelmingly Democratic over the decades. It's only with decreasing unionization in the region that whites in the surrounding counties and suburbs have grown more GOP friendly. Pittsburgh whites remain rather Democratic, between a combination of lingering union strength and hipster artsie social liberalism.
Obama got 75% of the vote in 2012, while non-hispanic whites were 65% of the population. So, Obama must have had a fairly large majority of the white vote.
