Traffic.com provides color-coded traffic maps, accident, and construction info, and informs you of traffic jams or severe delays. You can even save your regular routes to see what's happening on particular roads then sync and save these routes to the Traffic.com website. All this, and it doesn't even cost you a penny.
The Traffic.com app is now available in the iTunes app store and can be downloaded from here.
To watch a demo of the app in action, just