Ancestry.com has just released the index to New York state for the 1940 US Census.
You can access the 1940 census on Ancestry at this link, or go right to their new 1940 census page. (Use the first link to browse images of the states not yet indexed.)
Additionally, they have just added the New York State Censuses for 1892, 1915, and 1925. They are also offering a special membership to New York residents to access all three of these databases plus other New York related databases for free. There is no indication for how long the special access is good.
Editor’s Note: The first step to the NY resident membership is to enter a NY zip code, so I tried it. Instructions suggest that you have to set up a free account. I was already logged in and gained access to the databases immediately. Again, no idea how long the access will last, but I’m sure it’s available at the Family History Library at any time.