After 72 years, we will finally see the 1940 federal census for the United States on April 2, 2012. Unlike other census years, this census will not be on microfilm. For the first time, the census has been digitized, and will appear on the NARA website, available free to all. Unfortunately, there will not be a name index. Until such indexes are created, one must know the Enumeration District, then search through that district for the names.
A number of organizations will be creating name indexes, including numerous pay sites, and my favorite, FamilySearch.org, a free site. Volunteers are always welcome to assist FamilySearch.org with their indexing efforts. Census input forms and strategies are being worked on now, however, NO ONE will have access to the actual census images until April 2, so all census indexing efforts will begin that day. There are numerous other documents being indexed at any given moment, so if you have the time to assist, your help would be greatly appreciated!
The Stephen P. Morse One Step Website provides some ED finding aids.
The NARA site provides more details on the 1940 census.