UPDATE: Here's the video (via Hot Air):
CNN has the video from a security camera near the 35W bridge that catches the collapse. It shows it in the typical four-frames-per-second style of security video, but it quite clearly catches the sequence of the collapse.
The bridge appears to break, as one might guess from the pattern of the rubble, not in the center but as the span goes over the water of the river. The center section drops straight down, and the video briefly shows the cars that went down with it. A few seconds later, that first third of the bridge follows it down. In that first couple of frames, the steel structure buckles dramatically.
One point to note: it does not show the entire span of the bridge. The collapse could have started on the right of the camera, which is not shown. That would be the south end of the bridge; the video looks north across the river. So far, this has not been YouTubed, but if it does I'll post it here.
UPDATE: Here's MnDOT's picture at the edge of the collapse:
UPDATE III: Paul from Wizbang correctly notes that the video looks south, not north, which can he determined by the 10th Street bridge in the view.