I think this is pretty cool to watch:
Live streaming video of I-40 in Raleigh-Durham, NC:
http://www.wral.com/traffic/video/6763278/ (http://www.wral.com/traffic/video/6763278/)
California's (http://video.dot.ca.gov/) cameras are also streamed live but without the annoying pre-roll advert.
IDOT has a couple near the river bridges in the St. Louis Metro:
http://www.stl-traffic.org/Default.aspx (http://www.stl-traffic.org/Default.aspx)
However, the site seems to be pretty picky on the needed software to view the streaming video; all but the MLK Bridge camera don't wok on all but one computer I've used recently.