1) Xiph.org: Xiph also hosts lossless versions of the Blender OpenMovie project's files.
(Thanks Xiph! Thanks Blender!) NOTE: Tears of Steel is the rare chance to get hands on the raw EXR image sequences of a movie (stored in ILM's OpenEXR format)

2) Video Quality Experts Group (VQEG) 3) Swedish Television (SVT) 4) Austrian Mediathek 5) European Broadcasting Union (EBU)
NOTE: The EBU sequences can not be used for official, publicly reproducible tests, due to their licensing restrictions.
Excellent idea, to restrict test-videos to a small, exclusive group of members, so video experts, codec-developers and researchers are unable to share their results

UPDATE: The "Public Test Set" may be shared under Creative Commons (CC-BY-NC-ND) license.
I will only list them here for the sake of completeness.
If you can, please avoid using the EBU testvideos, and rather use material which is available to others, too.