Grand Central Taxi Stands
There is one main stand for Grand Central Terminal at East 42nd Street at Vanderbilt Avenue staffed by a taxi dispatcher 7 days a week from 7 AM to 11 PM. You can also try to hail a cab on the street though depending on time of day, that can be more challenging. There are many ride share services (INSERT LINK) as well that you can utilize such as Uber, Lyft, and a few others.
42nd Street and Vanderbilt Ave
Outside the main concourse on 42nd Street, there is a stand at the northeast corner of 42nd Street and Vanderbilt Ave.
See the yellow stand with lights in the Google Map Street View.