Many genealogists are familiar with the free website, Internet Archive, as a free source of digitized books and historical texts. Many, however, don't realize that you can also use this site to access digitized copies of many genealogical records, also for free! Just check out the U.S. census images, for example, scanned from microfilm from the collections of the Allen County Public Library. Federal decennial censuses are available 1790-1930 as digitized image scans only -- no search available. Despite having full, searchable access to U.S. census records through other websites, I still turn to the Internet Archive U.S. census collection whenever I run into a hard-to-read census page; the copies are very often clearer and easier-to-read. If you're on budget, you can conduct your free census searches at FamilySearch.org, and then browse Internet Archive for the actual census image for any census to which FamilySearch does not include the full census images (e.g. 1910-1930). Sure it takes some time to browse to the correct page but heck, I can do it from home in my pajamas for free. What's there to complain about?
A variety of other great collections of genealogical interest can be found under Ebook and Texts Archive -> Additional Collections -> Genealogy, which includes vital statistics, parish records, and other historical and biographical documents digitized from the genealogical collections of the Allen County Public Library in Fort Wayne, Indiana; Robarts Library at the University of Toronto; the University of Illinois Urbana-Champaign Library; the National Library of Scotland; and the Boston Public Library. Many of these -- such as U.S. passenger lists and passport applications -- are available elsewhere on subscription-based websites as searchable collections, but on Internet Archives the digitized images are free as long as you are willing to browse the records. Available collections cover the gamut from Scottish directories to Records of the Cotton Bureau of the Trans-Mississippi Department of the Confederate War Department. Of course there are also many genealogically relevant texts that aren't necessarily classified under the genealogy collection. Duke University Libraries, for example, has uploaded a large collection of Confederate imprints to Internet Archive, ranging from broadsides to General Orders.
Due to the vast amount of data available on Internet Archive, learning how to effectively focus your search can often be critical to finding content relevant to your research. Learn more about the types of content that can be found in Internet Archive, plus the search methods that provide the best results in my Guide to Research in the Internet Archive.