Well, I have 3 places that you should checkout! These are not the huge sites that want to charge mass money for a 30 second clip; in fact you can use the footage for free. (I have found lots of sites that have video footage, but I don't want to just make a huge list without really checking them out.)
Ok, you do not have to pay for it, but I am a firm believer in giving full credit to anyone whose work you use.
Click over to http://mitchmartinez.com and see some very cool stuff. Clouds, fireworks, moons and more is in the Free section as I write this!
You should also see http://www.beachfrontbroll.com A small site with some great footage. It has everyday things that you could use in lots of your videos!
And this site doesn’t have a lot of footage yet, but I am hoping the build! So, keep an eye on http://www.ignitemotion.com
Here is a Hot Blog Tips Hangouts on Air that we did about using video clips -
Watch on youtube.com
I will add to this list as I checkout more sites!