Looking at free databases on http://www.searchforancestors.com/ancestryfreebies.html, I see several interesting databases but most are already free on http://rootsweb.com/. To test it out I tried the WWI Civilian Draft Registrations. I had to register which was easy enough (just had to give a name and email address), but only got an index and only 1 of 3 brothers came up. So it is not as complete as the pay database, but worth taking a look at.
Update: I just got my 1st Ancestry SPAM from signing up. If you want to try this be warned!!!