NASA has a huge media library, full of images, sounds and video, which you can access for free and use as you wish.
NASA has occasionally offered one small part video and images to the public, but recently, brought your entire library to your disposal, through its website. There you can search by some term, just like you do on Google.
For example, a search for Pluto returns 543 different results, including a large number of images, nineteen videos, and nine archives audio. Most results also include a short description with each video, photo or clip so you know what you're looking at.
If you are looking for something specific, the searching results they can also be reduced by year. The oldest content available on the NASA site is from 1920, while the most recent content is from the current year. A slider allows you to select the desired time window for your search, or you can leave it wide open to see all the material NASA has.
The best part is that you can use the collection as you wish. There are rules for non-commercial use of NASA multimedia, which according to them content is generally not copyrighted. You may use this material for educational or informational purposes, including collections of photographs, textbooks, public exhibits, computer simulations, and Internet Web sites. This general license extends to personal websites.
If you want to use the content commercially it is not so easy and requires contacting NASA Multimedia Division in Washington DC.
