While researching various stock footage sites I stumbled upon this one unique site-Pond 5. What makes this website more unique as opposed to other similar services is both the fact that the prices on each clip are within reason and that once purchased you can pretty much do anything you want with it. You can insert a clip into your flick and make as many copies you want. There are no other licenses needed or anything.
Also helpful is the search bar which is set up into various categories and tags to allow you to find almost anything you may need for your next upcoming flick. Check it out here.