This website includes a collection of free space images, videos, animations, etc. It's a work in progress with new material being added most weeks.
All images at this website are in the public domain. Although this is not the same as copyright-free, it does mean that you can pretty much use the images as you please. Copyright is retained by organizations such as NASA, but you are allowed unlimited personal and commercial use. The only real condition is that you don't use images to imply a relationship with the copyright holder (such as product endorsement, etc).
All the images here are clean — no tacky watermarks or logos! Most are available in medium and high resolution.