This map from Accuweather.com shows where the rain has fallen in the last 24 hours. It is updated every hour.
Update – 9/15/2013: I have been watching the amounts of rainfall reported by Accuweather quite closely this season, and comparing them to other radar and ground-station reports. It appears that their estimates are around two or three times greater than reality. Accuweather shows the places where rain has fallen to a reasonable degree of accuracy, but take its quantitative estimates with a large grain of salt.