Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
I haven't been able to find an online open source of US neighborhoods with their corresponding zip codes. I am particularly looking for New York and Los Angeles.
You can use/combine Code for America's Click That 'hood with Zillow Neighborhood Boundary Shapefiles to get some, if not all of that data. Data is here:
Click That 'hood Data Directory
California Neighborhood Boundaries
New York Neighborhood Boundaries
Required, but never shown