I don’t know when this one was introduced, it seemed to slip in under the radar, but Yahoo! has added traffic condition and incident reports to Yahoo! Maps. Maps now display little colored icons indicating reported traffic speed and incident severity, mouse-over the icon for a popup containing details, and click for more information. Traffic data is available for over 40 major cities, details at http://maps.yahoo.com/traffic.
I noticed this recently as well. I created a "quick search" in firefox so I can enter "traffic zipcode" to get a heads up on my comuute before leaving the office.
http://beta.philcruz.com/blog/2004/12/traffic-quicksearch.htm