Much of the city is accessible with curb cuts for wheelchair users. All the major sites (the Met museum, the Guggenheim, and Lincoln Center) are also accessible. Some, but not all, Broadway theaters are accessible.
Unfortunately, only about 100 of New York's 468 subway stations are fully wheelchair accessible. In general, the bigger stations have access, such as West 4th St, 14th St-Union Sq, 34th St-Penn Station, 42nd St-Port Authority Terminal, 59th St-Columbus Circle, and 66th St-Lincoln Center. For a complete list of accessible subway stations, visit http://web.mta.info/accessibility/stations.htm. Also visit www.nycgo.com/accessibility.
On the plus side, all of NYC's MTA buses are wheelchair accessible, and are often a better option than negotiating cramped subway stations.
The city also provides paratransit buses for getting around town for the same price as a subway fare, though these aren't very practical as you must order them 24 hours in advance. Call Access-a-Ride (877-337-2017) to request transport.
More practical is simply ordering an accessible taxi through Accessible Dispatch (646-599-9999; http://accessibledispatch.org); there's also an app that allows you to request the nearest available service.
Another excellent resource is the Big Apple Greeter program, which has more than 50 volunteers on staff with physical disabilities who are happy to show off their corner of the city.
Download Lonely Planet's free Accessible Travel guide from http://lptravel.to/AccessibleTravel.