Probably not too well known to genealogists, digitized images of the entire US Census, including all the supplementary schedules, documentation etc., has been online for free from Archive.org. To see the US Census records go to the home page and look for the Text records on the lower right. There is a link to Browse and that takes you to a list of all of the U.S. Census images. The format is entirely different than any of the other U.S. Census images previously available online. Essentially, each roll of microfilm from the National Archives has been digitized as is. From some standpoints this is very, very good. For example, you get the feel of how the Census was combined into the various volumes. On the other hand, the census records are just that, the records. There is no searchable index to the images. But wait. Family Tree Magazine in an article that just came out with the December 2012 issue quotes Archive.org as saying that indexes are being added.
So where are the indexes? What isn't explained in the article is that the indexes they are referring to is a digitized copy of the Microfilm of the soundex card index to the U.S. censuses of population as collected by the Census Office. Yes, strictly speaking there is an index, but the index is the one done by the U.S. Census office. The really good news is that these soundex cards are being indexes so that they can be searched online. The Mesa Regional Family History Center, the Family History Library and some other locations have had the bound volumes of these indexes for a long time. On occasion, I have found names in the bound indexes that I have not found in either Ancestry.com or FamilySearch.org, but lately, I have really neglected to use this additional valuable resource, probably just because it wasn't on my computer. (Duh).
OK, so what does this all mean? It means that those of us too poor or too cheap to use Ancestry.com, can now have our own online free U.S. Census with an index. Pretty neat? Yeah. Now, it is not so convenient to use as Ancestry.com but here is another point, it is an entirely different copy and index to the Census. You just might find things in Archive.org that you can't find in the U.S. Census on any other source.
While you are looking at the Census, check out the rest of Archive.org's books and other media. You might just start visiting this site more often.