The GANYC PR Committee has been working to compile a comprehensive of NYC museums & cultural institutions that offer complimentary admission to anyone with a valid sightseeing guide license. Here is what we have. Please let us know if a) any of these are not correct, and b) we are missing any.
There are other institutions that may allow it on a case-by-case basis, but for the purposes of this list, we have only included those that have an official policy on it.
(This is not counting pay-what-you-wish places-- like the Metropolitan Museum of Art, Brooklyn Museum, Museum of Natural History-- where New York City residents can get in for low price or free if they so choose.)