NASA’s Earth Observatory has satellite images and animations of the weather system that spawned so many tornadoes this week.
Google Maps’s collection of tornado maps and images. The Wall Street Journal’s map of storm reports. Another map of storm reports.
MSNBC’s tracking map showing the path of the weather system along which tornadoes bloomed. A New York Times map showing hour-by-hour tornado reports.
Satellite and aerial images from before and after the tornadoes: the New York Times’s interactive maps (with the clever slider); a gallery of images from Google.