NASA TV UFOs: Excellent Compilation Video
The footage of the cylindrical shaped (or is it a disk?) UFO which can be seen at 5:55 minutes into the video is noteworthy. One can clearly see that the unknown object flies towards the Space Shuttle before it takes off in the opposite direction.
The video also includes remarkable statements by several U.S. astronauts:
http://www.youtube.com/watch?v=xWvK9mSr5IU
Some of the UFO videos (links) have been posted on this blog earlier.