Detroit, Baltimore, New Orleans, and Newark are the cities that immediately spring to mind.
newark is mostly bad in the projects, though it spills out into downtown after dark.
I worked in Newark for about 3 years, working late shifts (typically getting out of work around 12-1 am). downtown newark isn't that bad during the daylight hours, when businesses are open and the whole area is crawling with cops, but coming out of work, I'd walk to my car as quickly as possible, keep my head down, and GTFO of the city as quickly as possible, never turning off the main drags. eventually, I started paying $300/month for parking just to avoid being out on the streets (there was an underground/enclosed private parking lot in my office building that had direct elevator access upstairs). this was downtown, so it wasn't that bad, but you couldn't pay me to go through the projects at night.
NYC has been pretty well gentrified.