Update: Nixlog has a growing collection of infographics and interactive graphics related to the crash.
Update: some eyewitness photos (hard to get good photos at that distance...)
Update: Timeline of Columbia's last mission (another timeline).
Update: "Nick has access to orbital data for various satellites and other objects. He and Chris started looking at the data before it got locked up, and it appears that Columbia pulled up around 3 am, and continued to erratically change its path." (Juby)
Update: video of NASA TV broadcast when NASA lost contact with Columbia. Video of NASA trying to reestablish communication with Columbia.
Update: a radar image of Shuttle debris over Texas.
Update: NASA says a piece of foam that impacted the left side of the shuttle on takeoff may be to blame, but unlikely. I mean, how much damage can a piece of foam do? I guess we'll know more when we get a look at what that foam actually looks like.
A Space Shuttle contingency has been declared in Mission Control, Houston, as a result of the loss of communication with the Space Shuttle Columbia at approximately 9 a.m. EST Saturday as it descended toward a landing at the Kennedy Space Center, Fla. It was scheduled to touchdown at 9:16 a.m. EST.
Communication and tracking of the shuttle was lost at 9 a.m. EST at an altitude of about 203,000 feet in the area above north central Texas. At the time communications were lost. The shuttle was traveling approximately 12,500 miles per hour (Mach 18). No communication and tracking information were received in Mission Control after that time.