The awesome thing about Maptime is there's like, a million amazing resources for learning about mapping and maps. The awesome thing about working on mapping stuff in New York is that there's also a ton of data resources for maps. Here's a list of both things!
Bytes of the Big Apple: Run by NYC's Department of City Planning, it mostly has a lot of the same datasets you can find on the Open Data Portal but usually has more detailed metadata for its datasets. This is where you can download MapPLUTO! And historical MapPLUTO!
NYC Open Data Portal: The City of New York's Official open data portal--has a ton of datasets, some of which are honestly more useful than others. Disadvantages: usually limited metadata, harder to get context for a given dataset. Honestly, I tend to go to this site as a last resort.
ACRIS: also known as the Automated City Register Information System (ACRIS). A kind of clumsy to use resource for a deeper dive on real estate data for specific properties. Like all portals, it makes you kind of die inside, but it means well.
The one MTA subway shapefile that, pretty much, everyone ends up finding via Google). This was made by Steve Romulewski. All hail Steve.
BetaNYC's Github: BetaNYC is an open data, open government, and civic technology community group. They are a part of Code for America's brigade program and hosts useful datasets that might not be easily or immediately found on the city's open data portal. They also have a spreadsheet of data resources that you might enjoy. You can learn more about getting involved with their meetups and at their Meetup page or check out their mailing lists and discussion groups.
MTA Developer Resources: Pretty much what it sounds like. There's a variety of real-time and static data feeds including GTFS Schedule Data, bus and subway times, fare data, subway entry and exit spatial data, and turnstile usage data.
NYC Geoclient API: Also maintained by the Department of City Planning, the Geoclient API lets developers geocode using Geosupport, the city's in-house geocoder.
NYS GIS Clearinghouse: It's what it sounds like. Honestly, I still find this site really overwhelming and confusing and would love to spend more time actually looking at what's even there.