Try www.archive.org

There is another too I know of, but it has escaped me. I'll get back to you on that one.

Hey, I'm just curious: how do you use the site? I'm kinda confused by it.

Well, although I haven't actually used it myself, I think it goes a little like this:
Say you are looking for footage of an explosion, you would type that keyword into the searchbar. Then it should come up with a whole heap of uncopyrighted materials that you can download and use in your film.
Let us know if it isn't working for you.

I have a question related to this that I don't know if someone knows the answer.

Let's say there is a film in the public domain (for a simple example we'll make it Cary Grant's "My Girl Friday"). Now this film is even available on archive.org for free download.

Let's say further that this film can be picked up for a buck at the dollar store (which it can). Is it legal to take the footage off the DVD and use it in a film? Or does the DVD producer have a new copyright on the transfer making it off limits? Anyone have any idea?

Dan Rahmel
Author: "Nuts and Bolts Filmmaking"
http://www.cvisual.com

I think you'd probably have to get the copyrights for it, although I was copyrighting something and theres a space where it says "existing materials" for things that already have copyright but you dont have them.