I was wondering if there is a site where I can view the united states public records index?
Like the one you would find on ancestry.com only for FREE
Ancestry.com built that database on their own by combining hundreds of public databases. Many of those records are available for free from the LDS at www.familysearch.org. The SSDI is available free on Rootsweb at http://ssdi.rootsweb.com/cgi-bin/ssdi.cgi. Property records are usually available for free from the local county clerks’ offices or their websites. Some do make you go into their offices to do detailed searches in person, but many many have searchable databases on the www.
Military records are available through the National Archives, but are not online for free as a whole. Many groups, such as the Sons of the American Revolution, have their parts of it online for free or will do free lookups for you.
So the basic answer is that Ancestry is kind enough to bring all of these pieces together for you, but for a fee. If you want free copies of these resources, you need to do the leg work yourself and find the ones you want in person.