Depending on when you leave the house, traffic can vary from manageable to an absolute nightmare. When2Leave helps you leave at the best time by sending you an alert when traffic dies down. This web app is especially useful for people who actually have some flexibility with their schedules. You simply type your origin and destination into the app, then tell it to notify you when the route falls below whatever amount of time you desire. It will tell you what the average and current traffic time is for the route.
It's only available via your browser, though, so you have to be at your computer to get the alert. It would be even more useful as a mobile app, and the founders are in the process of developing one. However, it still works well if you're on your computer. If you're at work, for example, and trying to figure out the best time to leave at the end of the day, the app will send a pop-up telling you that your route is within your time frame.
Of course, you can always check Google Maps for updates, but this offers a more automatic alternative than refreshing Maps every so often. Check it out for yourself at the link below.