Yes. There is a wealth of material out there that either is in the public domain or is available under what is known as a Creative Commons licence, which generally means the work is available for free but is subject to certain limited conditions, such as non-commercial use only and acknowledgement of the creator.
For materials available through a Creative Commons licence, visit the Creative Commons website for more information or check out its content directories that list audio, video, image, and text materials available under a Creative Commons licence. For material in the public domain, simply search online for "public domain" and the type of material you’re interested in. Some useful sites include: Project Gutenberg (the largest collection of copyright-free books online) and Wikipedia, which has an entire page dedicated to public domain resources.
For other online materials, a recommended best practice is to check the website's "Terms of Use", or "Legal Notices" statement to confirm what conditions apply to the use of the website's material. In many cases, you may be able to use the material for free for non-commercial and educational purposes.