This information might be a little bit dated, but as long as the govt. is providing a useful service it might as well be publicized.
In August of 2008 the U.S. Citizenship and Immigration Services, formerly INS, established a Genealogy Program. Genealogists can request records of genealogical interest to be searched for and copied. The service is dedicated to genealogists, historians and other researchers seeking records that generally do not require FOIA expertise. This is a fee for service program. A genealogy index search is $20, copy of a file on microfilm is $20 and a copy of a textual file is $35.
The USCIS Genealogy Program offers two services:
Index Search: Using biographical information provided by the researcher, USCIS searches its historical immigration and naturalization record indices for citations related to a specific immigrant. Search results (record citations) are returned to the researcher, along with instructions on how to request the file(s) from USCIS or the National Archives. Fee: $20.00.
Record Copy Request: Researchers with valid record citations (USCIS file numbers), gained through a USCIS Genealogy Program index search or through independent research, may request copies of historical immigration and naturalization records. Fee: $20.00/$35.00 (depending on the record type).
Records available through the USCIS Genealogy Program:
Naturalization Certificate Files (C-files) from September 27, 1906 to April 1, 1956
Alien Registration Forms from August 1, 1940 to March 31, 1944
Visa files from July 1, 1924 to March 31, 1944
Registry Files from March 2, 1929 to March 31, 1944
Alien Files (A-files) numbered below 8 million (A8000000) and documents therein dated prior to May 1, 1951
When their website was last updated on 30 Oct 2009 they were answering requests from early Oct 2009. With the current events in Haiti there might be a greater delay.
If you are interested in seeing what they have available the main website is at www.uscis.gov. On their Home page the link for Genealogy is at the bottom of the left hand column. If you are not interested in seeing what else USCIS has to offer use this link to go directly to Genealogy.