These search tools will help you find material that you can use responsibly. Make sure you give credit to the creator.
The obvious one is the CC Search. This site is run by the CC folks. You can filter by type of license and one day they plan to have music and video search results.
If you click on the tab for audio or video it will provide you with some CC-friendly search options, but I think the ones on this page are better options.
Ben Sound is a website with great options for royalty-free music. Search by the type of music you want. Look for the Download label under the song (some of the songs have Purchase labels).
Click on the image with the song and you will find the download tab and the conditions for use. Most simply ask that you include attribuion that you found the song on this website.
There are a number of options for images. Student access to the sites changes with updates to the filter, so they might not all work for you. Also, you will find that the sites will often return a lot of the same results. They are not four separate databases.
The Digital Public Library of America is similar, but slightly different. It contains works that are in the public domain, meaning that no one owns them. You can use anything you find here.