Users of the incredibly useful Google Maps service probably noticed a new button added to the interface recently.  Previously only available via the mobile client, desktop users now have access to a "Traffic" button that will draw an overlay on roads indicating their current traffic load.  Green means that traffic is moving at least 50 miles per hour or higher, yellow is 25 - 50 miles per hour, red is less than 25 miles per hour, and gray indicates there's no data available.

Of course, coverage is not complete in all areas.  Here in the Detroit area it only covers the major highways and interstates, and entire swatches of Pennsylvania have no traffic data available period.  Plug in your zip code and see what Google comes up with for you.