Not all car manuals are available for free, but one useful resource, JustGiveMeTheDamnManual.com, hosts over 2,000 PDFs of different user manuals for a range of makes and models. Other options for finding a free manual include visiting the manufacturer's website or trying a general manuals source, such as Manuals Online.
Edmunds.com provides links to a range of manufacturers' manuals on their own websites, with a focus on American models. This can help to reduce search time. All of the available options for free manuals are available only in virtual form. Paper copies, both new and used, are available for a fee.