Censuses, Passports, Manifests
Many documents that the U.S. goverment collects are released for public consumption after a certain number of years. These documents are a treasure trove for genealogists.
Available at U.S. National Archive locations (on microfilm and/or in original documents), these documents are often easier to access through multiple, commercial (paid subscription) websites. I find ancestry.com to be the best source. Ancestry’s scans are high-resolution and clear, their servers are fast, and they have the most accurately typed (or, perhaps, most accurately proofread) data.
They also have an interactive system that allows users to type in "suggested spellings" of peoples names which is useful in several ways. If your relative’s name was transcribed incorrectly by a database programmer (who is often reading from a hand-written document), or if it was entered incorrectly in the original document (which is common with census reports), there’s a chance someone else has corrected it. This might help you find the name you want. Or, through the comments, you might find another user who is a far-flung member of your own family.
U.S. National Archives
As a backup, or if you want to check the actual original documents in case something wasn’t scanned by ancestry.com, many federal records for the New York region are available at the regional office of the U.S. National Archives on Hudson Street in lower Manhattan.
The archivists in this office are terrific. I used this resource for some court documents I couldn’t find elsewhere; the archivist explained the different types and levels of courts very clearly and gave me the addresses and phone numbers of non-federal courts where I should also look. In other words, he wasn’t locked in his federal "silo." He knew all the other court archives in New York City.
Visiting this office reminds me how my "too-big" federal government (say some, but not me!) provides this terrific service to me, the tax-payer.